Molecular Cancer Research最新文献

Atypical teratoid rhabdoid tumor (ATRT) is a highly aggressive pediatric brain tumor driven by the loss of SMARCB1, which results in epigenetic dysregulation of the genome. SMARCB1 loss affects lineage commitment and differentiation by controlling gene expression. We hypothesized that additional epigenetic factors co-operate with SMARCB1 loss to control cell self-renewal and drive ATRT. We performed an unbiased epigenome targeted screen to identify genes that co-operate with SMARCB1 and identified SIRT2 as a key regulator. Using in vitro pluripotency assays combined with in vivo single cell RNA transcriptomics, we examined the impact of SIRT2 on differentiation of ATRT cells. We employed a series of orthotopic murine models treated with SIRT2 inhibitors to examine the impact on survival and clinical applicability. We found that ATRT cells are highly dependent on SIRT2 for survival. Genetic or chemical inhibition led to decrease cell self-renewal and induction of differentiation in tumor spheres and in vivo models. We found that SIRT2 inhibition can restore gene expression programs lost due to SMARCB1 loss and reverse the differentiation block in ATRT in vivo. Finally, we showed the in vivo efficacy of a clinically relevant inhibitor demonstrating SIRT2 inhibition as a potential therapeutic strategy. We concluded that SIRT2 is a critical dependency in SMARCB1 deficient ATRT cells and acts by controlling the pluripotency-differentiation switch. Thus, SIRT2 inhibition is a promising therapeutic approach that warrants further investigation and clinical development. Implications: SIRT2 inhibition is a molecular vulnerability in SMARCB1-deleted tumors.

Approximately 97% of the human genome comprises non-coding sequences, with nearly half originating from transposable elements. Among these, retrotransposons represent a critical subclass that replicates via a "copy-and-paste" mechanism and significantly influences the regulation of host genomes. In both normal and pathological contexts, retrotransposons contribute a vast reservoir of regulatory elements that can modulate the expression of genes. If left unchecked, retrotransposons can substantially affect host transcriptional programs and genomic integrity. Therefore, various mechanisms, including epigenetic modifications, are employed to mitigate their potentially deleterious effects. In diseases such as cancers, the epigenome is often significantly reprogrammed, which can lead to retrotransposon dysregulation. Drawing insights from recent studies conducted in human and murine cells, this review examines how retrotransposons expand the complexity of mammalian genomes, describes the impact of their epigenetic dysregulation in cancer development, and highlights the potential of targeting these sequences for therapeutic strategies.

Small-cell lung cancer (SCLC) has a dismal five-year survival rate of less than 7%, with limited advances in first line treatment over the past four decades. Tumor-initiating cells (TICs) contribute to resistance and relapse, a major impediment to SCLC treatment. Here, we identify Kinase Suppressor of Ras 1 (KSR1), a molecular scaffold for the Raf/MEK/ERK signaling cascade, as a critical regulator of SCLC TIC formation and tumor initiation in vivo. We further show that KSR1 mediates cisplatin resistance in SCLC. While 50-70% of control cells show resistance after 6-week exposure to cisplatin, CRISPR/Cas9-mediated KSR1 knockout prevents resistance in >90% of SCLC cells in ASCL1, NeuroD1, and POU2F3 subtypes. KSR1 KO significantly enhances the ability of cisplatin to decrease SCLC TICs via in vitro extreme limiting dilution analysis (ELDA), indicating that KSR1 disruption enhances the cisplatin toxicity of cells responsible for therapeutic resistance and tumor initiation. The ability of KSR1 disruption to prevent cisplatin resistant in H82 tumor xenograft formation supports this conclusion. Previous studies indicate ERK activation inhibits SCLC tumor growth and development. We observe a minimal effect of pharmacological ERK inhibition on cisplatin resistance and no impact on TIC formation via in vitro ELDA. However, mutational analysis of the KSR1 DEF domain, which mediates interaction with ERK, suggests that ERK interaction with KSR1 is essential for KSR1-driven cisplatin resistance. These findings reveal KSR1 as a potential therapeutic target across multiple SCLC subtypes. Implications: Genetic manipulation of KSR1 in SCLC reveals its contribution to cisplatin resistance and tumor initiation.

Activation of lineage-specific gene expression programs is mediated by recruitment of lineage-specific transcription factors and their coactivators to chromatin. The lineage factor PAX8 drives essential gene expression in ovarian cancer cells and is required for tumor proliferation. However, the molecular details surrounding co-factor recruitment and specific activation of transcription by PAX8 remain unknown. Here, we identify an important functional interaction between PAX8 and the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex. We show that PAX8 can recruit SWI/SNF complexes to DNA, where they function to open chromatin and facilitate expression of PAX8 target genes. Genetic deletion of PAX8 results in loss of SWI/SNF from PAX8 bound enhancers, loss of expression of associated target genes, and reduced proliferation. These results can be phenocopied by pharmacological inhibition of SWI/SNF ATPase activity. These data indicate that PAX8 mediates the expression of an essential ovarian cancer proliferative program in part by the recruitment of the SWI/SNF complex, highlighting a novel vulnerability in PAX8 dependent ovarian cancer. Implications: PAX8 recruits SWI/SNF complexes to enhancers, to mediate expression of genes essential for ovarian cancer proliferation.

Triple-negative breast cancer (TNBC) presents significant clinical challenges due to its limited treatment options and aggressive behavior, often associated with poor prognosis. This study focuses on Kindlin-2, an adaptor protein, and its role in TNBC progression, particularly in hematopoiesis-mediated immune evasion. TNBC tumors expressing high levels of Kindlin-2 induce a notable reshaping of hematopoiesis, promoting expansion of myeloid cells in bone marrow (BM) and spleen. This shift correlated with increased levels of neutrophils and monocytes in tumor-bearing mice over time. Conversely, genetic knockout of Kindlin-2 mitigated this myeloid bias and fostered T cell infiltration within the tumor microenvironment, indicating Kindlin-2's pivotal role in immune modulation. Further investigations revealed that Kindlin-2 deficiency led to reduced expression of PD-L1, a critical immune checkpoint inhibitor, in TNBC tumors. This molecular change sensitized Kindlin-2-deficient tumors to host anti-tumor immune responses, resulting in enhanced tumor suppression in immune-competent mouse models. Single-cell RNA sequencing, bulk RNA-seq, and immunohistochemistry data supported these findings by highlighting enriched immune-related pathways and increased infiltration of immune cells in Kindlin-2-deficient tumors. Therapeutically, targeting PD-L1 in Kindlin-2-expressing TNBC tumors effectively inhibited tumor growth, akin to the effects observed with genetic Kindlin-2 knockout or PD-L1-KO. Our data underscore Kindlin-2 as a promising therapeutic target in combination with immune checkpoint blockade to bolster anti-tumor immunity and counteract resistance mechanisms typical of TNBC and other immune evasive solid tumors. Implications: Kindlin-2 regulates tumor immune evasion through the systemic modulation of hematopoiesis and PD-L1 expression, which warrants therapeutic targeting of Kindlin-2 in TNBC patients.

The E3 ubiquitin ligase RNF6 has been widely recognized for its role in promoting tumorigenesis in multiple cancers. However, we found it is downregulated in lung adenocarcinoma (LUAD) and the molecular rationale for this discrepancy remains unclear. In the present study, we find that RNF6 but not its ΔRING inactive form inhibits LUAD cell proliferation and migration and sensitizes LUAD to chemotherapy. To understand the molecular mechanism, we utilize affinity purification/tandem mass spectrometry to analyze RNF6-interacting proteins and find that cyclin D2 (CCND2), a key regulator of the G1/S transition in the cell cycle. RNF6 physically binds to CCND2 and mediates its K48-linked polyubiquitination and subsequent degradation. However, ΔRING RNF6 fails to mediate CCND2 for ubiquitination and degradation. Moreover, Thr280 is critically important for CCND2 stability. When Thr280 is mutated, CCND2 becomes more stable and less ubiquitinated by RNF6. Furthermore, RNF6 arrests LUAD cell cycle at the G1 phase by inhibiting the CCND2/pRb signaling pathway, which is consistent with decreased cell proliferation. Lastly, RNF6 curtails the growth of LUAD xenografts in vivo, associated with decreased CCND2 expression. Therefore, RNF6 is a novel E3 ligase of CCND2 and suppresses LUAD cell proliferation. Implications: This study reveals a novel regulation on cell cycle transition in LUAD and suggests the RNF6/CCND2 axis may represent an alternative therapeutic target for the treatment of LUAD.

TIPE is a protein highly expressed in various cancers that promotes ferroptosis in colorectal cancer cells. Ferroptosis is a nonapoptotic cell death caused by lipid peroxidation, and microsomal glutathione transferase 1 (MGST1) is a critical enzyme that resists lipid peroxidation. This study explored how TIPE regulates MGST1 expression to inhibit ferroptosis and promote colorectal cancer proliferation. TIPE was highly expressed in colorectal cancer tissues and positively correlated with the proliferation of human colorectal cancer cells. We measured levels of reactive oxygen species and lipid reactive oxygen species in colorectal cancer cells with differential expression of TIPE and detected ferroptosis using transmission electron microscopy. Bioinformatics analysis revealed a positive correlation of expression patterns between TIPE and MGST1 in colorectal cancer. TIPE regulated the expression of MGST1 by activating the phosphorylation of ERK1/2. Coimmunoprecipitation revealed binding between MGST1 and ALOX5. This binding inhibited the phosphorylation of ALOX5, inhibiting ferroptosis and promoting the proliferation of colorectal cancer cells. A tumor formation experiment in nude mice supported our findings that TIPE regulates the proliferation of colorectal cancer by regulating ferroptosis. Implications: TIPE inhibits colorectal cancer ferroptosis via an MGST1-ALOX5 interaction to promote colorectal cancer proliferation. These findings suggest future colorectal cancer treatment strategies.

Colorectal cancer tumors start as polyps on the inner lining of the colorectum, in which they are exposed to the mechanics of peristalsis. Our previous work leveraged a custom-built peristalsis bioreactor to demonstrate that colonic peristalsis led to cancer stem cell enrichment in colorectal cancer cells. However, this malignant mechanotransductive response was confined to select colorectal cancer lines that harbored an oncogenic mutation in the Kirsten rat sarcoma virus (KRAS) gene. In this study, we explored the involvement of activating KRAS mutations on peristalsis-associated mechanotransduction in colorectal cancer. Peristalsis enriched cancer stem cell marker Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) in KRAS mutant lines in a Wnt ligand-independent manner. Conversely, LGR5 enrichment in wild-type KRAS lines exposed to peristalsis were minimal. LGR5 enrichment downstream of peristalsis translated to increased tumorigenicity in vivo. Differences in mechanotransduction were apparent via unbiased gene set enrichment analysis, in which many unique pathways were enriched in wild-type versus mutant lines. Peristalsis also triggered β-catenin nuclear localization independent of Wnt ligands, particularly in KRAS mutant lines. The involvement of KRAS was validated via gain and loss of function strategies. Peristalsis-induced β-catenin activation and LGR5 enrichment depended on the activation of the MEK/ERK cascade. Taken together, our results demonstrated that oncogenic KRAS mutations conferred a unique peristalsis-associated mechanotransduction response to colorectal cancer cells, resulting in cancer stem cell enrichment and increased tumorigenicity. These mechanosensory connections can be leveraged in improving the sensitivity of emerging therapies that target oncogenic KRAS. Implications: Oncogenic KRAS empowers colorectal cancer cells to harness the mechanics of colonic peristalsis for malignant gain independent of other cooperating signals.

Approximately 70% of oropharyngeal squamous carcinomas (OPSCC) are associated with human papillomavirus (HPV). Although patients with HPV-positive (HPV+) tumors generally have better outcomes than those with HPV-negative tumors, a subset of HPV+ positive patients do have poor outcomes. Our previous work suggested that tumors with integrated virus exhibit significantly greater genome-wide genomic instability than those with only episomal viral genomes, and patients with HPV+ OPSCC with episomal viral genomes had better outcomes. To explore the causal relation between viral integration and genomic instability, we have examined the time course of viral integration and genetic instability in tonsillar keratinocytes transformed with HPV16. HPV-infected human tonsil keratinocyte cell lines were continuously passaged, and every fifth passage, some cells were retained for genomic analysis. Whole-genome sequencing and optical genomic mapping confirmed that virus integrated in five of six cell lines while remaining episomal in the sixth. In all lines, genome instability occurred during early passages but essentially ceased following viral integration; however, it continued to occur in later passages in the episomal line. To test tumorigenicity of the cell lines, cells were injected subcutaneously into the flanks of nude mice. A cell line with the integrated virus induced tumors following injection in the nude mouse whereas that with the episomal virus did not. Implications: Genomic instability in HPV OPSCC tumors is not the result of viral integration but likely promotes integration. Moreover, transformants with episomal virus seem to be less tumorigenic than those with integrated virus.

Cholangiocarcinoma (CCA) is a rare cancer that arises from the bile duct and is broadly classified by the location of the tumor as either intrahepatic cholangiocarcinoma (iCCA) or extrahepatic cholangiocarcinoma (eCCA). Immunotherapy has revolutionized cancer treatment, yet its utility in CCA has been limited as the tumor microenvironment (TME) in CCA is poorly understood compared with other common cancers. Utilizing previously published transcriptome data, our reanalysis has revealed that CCA has one of the highest relative levels of NK cells, a potent cytotoxic immune cell, compared with other cancers. However, despite iCCA and eCCA having comparable relative levels of NK infiltration, NK cell infiltration only correlated with survival in patients with eCCA. Our subsequent investigation revealed that although iCCA and eCCA profoundly altered NK activity, eCCA had a significantly reduced impact on NK functionality. Whereas iCCA was resistant to long-term NK coculture, eCCA was markedly more sensitive. Moreover, although both iCCA and eCCA dysregulated key NK-activating receptors, eCCA coculture did not impact NKp30 nor NKp44 expression. Furthermore, tumor transcriptome analysis of NKHigh CCA samples revealed a modulation of multiple immune and nonimmune cell types within the TME. Implications: These studies are the first to investigate how iCCA and eCCA impact NK cell functionality through shared and distinct mechanisms and how elevated NK cell infiltration could shape the CCA TME in a subtype-dependent manner.