Molecular Cancer Research最新文献

Chromosomal instability in gastric cancer cells is associated with the amplification of oncogenes that encode receptor tyrosine kinases (RTK), such as HER2 and FGFR2; such gene amplification varies from cell to cell and manifests as genetic heterogeneity within tumors. The intratumoral genetic heterogeneity of RTK gene amplification causes heterogeneity in RTK protein expression, which has been suggested to be associated with therapeutic resistance to RTK inhibitors; however, the underlying mechanism is not fully understood. In this study, we show that extrachromosomal DNA (ecDNA) causes intratumoral genetic heterogeneity in RTKs and drug resistance due to diverse dynamic changes. We analyzed the dynamics of FGFR2 and MYC ecDNA in a gastric cancer cell line after single-cell cloning. Similar to those in parental cells, the copy numbers of FGFR2 and MYC in subclones differed significantly between cells, indicating intraclonal genetic heterogeneity. Furthermore, the ecDNA composition differed between subclones, which affected FGFR2 protein expression and drug sensitivity. Interestingly, clone cells that were resistant to the FGFR2 inhibitor AZD4547 presented diverse changes in ecDNA, including chimeric ecDNA, large ecDNA, and increased ecDNA numbers; these changes were associated with high expression and rephosphorylation of FGFR2. Conversely, when resistant clone cells were cultured under conditions that excluded AZD4547, the ecDNA status became similar to that of the original clone cells, and the inhibitory effect on cell growth was restored.

Implications: Our results show that dynamic quantitative and qualitative changes in ecDNA can drive the intratumoral genetic heterogeneity of RTKs and resistance to RTK inhibitors.

The six-transmembrane epithelial antigen of the prostate (STEAP; STEAP1 and STEAP2) metalloreductases are therapeutic targets for advanced prostate cancer, and their expression has been linked to androgen receptor (AR) signaling; however, the regulatory mechanism and functions of STEAP1 and STEAP2 in prostate cancer progression remain elusive. In this study, we explore how in vitro androgen modulation and AR inhibition influence the expression of STEAP family members in cell lines with varying reliance on androgen signaling. Our data show that in response to androgen deprivation, STEAP1 and STEAP2 exhibit elevated transcript levels, whereas STEAP4 levels are reduced, mirroring the expression profile of kallikrein-related peptidase 3 (KLK3). As STEAP1 and STEAP2 are implicated in the exocytic pathway, we evaluated expression profiles in small extracellular vesicles (sEV) released from prostate cancer cells and in circulating sEVs. STEAP1, but not STEAP2, is upregulated in sEVs from AR-negative cells, which express low cellular STEAP1, and AR-positive cells, which express high cellular STEAP1. These results indicate selective packaging of STEAP1 in prostate cancer cell-derived sEVs, irrespective of AR status and cellular STEAP1 expression levels. Finally, ex vivo analysis of circulating sEVs from genetically engineered mice carrying prostate cancer shows that STEAP1 is found in the sEV cargo and that its levels are independent of protumorigenic β1 integrin expression in the prostatic epithelium.

Implications: Understanding how androgen dependence affects STEAP1 expression in both tumor cells and sEVs across distinct disease stages will illuminate the clinical benefit of combinatorial AR and STEAP1-directed therapies and inform the optimal placement of STEAP1 targeting within the prostate cancer disease continuum.

Patients with triple-negative breast cancer (TNBC) and comorbid type 2 diabetes (T2D), characterized by insulin resistance of adipose tissue, have a higher risk of metastasis and shorter survival. Adipocytes are the main nonmalignant cells of the breast tumor microenvironment (TME). However, adipocyte metabolism is usually ignored in oncology, and the mechanisms that couple T2D to TNBC outcomes are poorly understood. In this study, we hypothesized that exosomes, small vesicles secreted by TME breast adipocytes, drive epithelial-to-mesenchymal transition (EMT) and metastasis in TNBC via miRNAs. Exosomes were purified from conditioned media of 3T3-L1 mature adipocytes, either insulin-sensitive (IS) or insulin-resistant (IR). Murine 4T1 cells, a TNBC model, were treated with exosomes in vitro (72 hours). EMT, proliferation, and angiogenesis were elevated in IR versus control and IS. Brain metastases showed more mesenchymal morphology and EMT enrichment in the IR group. MiR-145a-3p is highly differentially expressed between IS and IR and potentially regulates metastasis.

Implications: IR adipocyte exosomes modify the TME, enhance EMT, and promote brain metastasis-likely via miRNA pathways-suggesting that metabolic diseases such as T2D foster a prometastatic TME, reducing survival and warranting close monitoring and potential metabolic interventions in patients with TNBC and T2D.

Small cell lung cancer (SCLC) has a dismal 5-year survival rate of less than 7%, with limited advances in first-line treatment over the past four decades. Tumor-initiating cells (TIC) contribute to resistance and relapse, a major impediment to SCLC treatment. In this study, 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. Whereas 50% to 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 knockout significantly enhances the ability of cisplatin to decrease SCLC TICs via in vitro extreme limiting dilution analysis, 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 resistance in H82 tumor xenograft formation supports this conclusion. Previous studies indicate that ERK activation inhibits SCLC tumor growth and development. We observe a minimal effect of pharmacologic ERK inhibition on cisplatin resistance and no impact on TIC formation via in vitro extreme limiting dilution analysis. 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 key regulatory protein in SCLC biology and a potential therapeutic target across multiple SCLC subtypes.

Implications: Genetic manipulation of the molecular scaffold KSR1 in SCLC cells reveals its contribution to cisplatin resistance and tumor initiation.

Nerves are important components of the tumor microenvironment and can regulate the progression of various solid tumors. Tumor innervation (TIN) and perineural invasion (PNI) are the two main modes of interaction between tumors and the nervous system. The former simulates neurogenesis or axonogenesis during neural development, whereas the latter causes neuroinflammation during nerve injury. As the principal glial cells of the peripheral nervous system, Schwann cells (SC) are easily hijacked and utilized by cancer cells due to their high plasticity and versatility. Whether TIN or PNI occurs in a tumor, SCs are believed to be associated with these processes, which indicate that SCs may be a target for cancer neurotherapy. This review focuses on elucidating the interactions between tumors and the peripheral nervous system and the underlying mechanisms involved. Specifically, we delineated the pivotal role of SCs in TIN, PNI, cancer pain, and the immunosuppressive microenvironment. Furthermore, we compared the advantages and disadvantages of several preclinical trials that have exploited the nervous system to treat cancer and discussed the importance of SCs as a new target in cancer neuroscience research. We hope that this review will contribute to a deeper understanding of the significant involvement of SCs within the tumor-neuroimmune axis and provide novel insights for innovative antitumor therapies.

The malignant progression of human cancer is dictated by specific regulatory hubs coordinating multiple signaling modules. Identifying key oncogenic hubs of human cancers may lay the groundwork for developing breakthrough therapeutic strategies. Actin-like 6A (ACTL6A; also known as BAF53A) was originally identified as a chromatin remodeling factor involved in the transcriptional regulation of genes, especially in stem and progenitor cells. The preponderance of evidence revealed the overexpression of ACTL6A in most cancers and its crucial role in various malignant phenotypes, including cell-cycle progression, cancer stemness, epithelial-to-mesenchymal transition, redox and glucose metabolism, and DNA replication and repair. Interestingly, emerging data suggest that the oncogenic function of ACTL6A is mediated through diverse mechanisms beyond its canonical function in transcriptional regulation, including notably the stabilization of oncoproteins and stemness factors, such as YAP, VPS72, and MYC. In this review, we describe the isoforms and the putative functional domains of ACTL6A. We summarize the expression pattern and prognostic significance of ACTL6A in human cancers and the upstream regulatory mechanisms of its expression. We summarize recent progress in understanding the diverse pro-oncogenic functions of ACTL6A and emphasize its pleiotropic mechanisms of action as a regulatory hub of cancer stemness and progression. The review highlights the importance and the potential utilities of characterizing ACTL6A, which may imply molecularly informed diagnostics and therapeutics to improve the outcome of patients with cancer.

Cooperativity between mutant p53 and mutant KRAS, although recognized, is poorly understood. In pancreatic cancer, mutant p53 induces splicing factor hnRNPK, causing an isoform switch that produces overexpression of GTPase-activating protein 17 isoform 1 (GAP17-1). GAP17-1 is mislocalized in the cytosol instead of the membrane, owing to the insertion of exon 17 encoding a PPLP motif, thus allowing mutant KRAS to remain in the GTP-bound hyperactive state. However, the role of PPLP in influencing GAP17-1 mislocalization remains unclear. We show that Smad ubiquitination regulatory factor 2 (SMURF2), a known stabilizer of mutant KRAS, interacts with GAP17-1 via the PPLP motif and displaces it from the membrane, facilitating mutant p53-mediated mutant KRAS hyperactivation. We used cell lines with known KRAS and TP53 mutations, characterized SMURF2 expression in multiple pancreatic cancer mouse models (iKras*; iKras*, p53*, and p48-Cre; Kras*), and performed single-cell RNA sequencing and tissue microarray on preclinical and clinical samples. We found that SMURF2 silencing profoundly reduces the survival of mutant TP53; KRAS-driven cells. We show that a GAP17-1 AALA mutant does not bind to SMURF2, stays in the membrane, and keeps mutant KRAS in the GDP-bound state to inhibit downstream signaling. In mouse models, mutant KRAS and SMURF2 upregulation are correlated with pancreatic intraepithelial neoplasia and ductal adenocarcinoma lesions. Furthermore, patients with pancreatic ductal adenocarcinoma who received neoadjuvant therapy and express moderate-to-high SMURF2 show decreased overall survival (P = 0.04).

Implications: In TP53 and KRAS double-mutated pancreatic cancer, SMURF2-driven GAP17-1 membrane expulsion facilitates mutant p53-KRAS oncogenic synergy.

Activation of lineage-specific gene expression programs is mediated by the 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 cofactor recruitment and specific activation of transcription by PAX8 remain unknown. Here, we identify an important functional interaction between PAX8 and the switch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complex. We show that PAX8 can recruit SWI/SNF complexes to DNA, in which they function to open chromatin and facilitate the 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 the expression of genes essential for ovarian cancer proliferation.

Approximately 97% of the human genome comprises noncoding 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 pathologic contexts, retrotransposons contribute to 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, have been employed to mitigate their potentially deleterious effects. In diseases such as cancer, 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 on cancer development, and highlights the potential of targeting these sequences for therapeutic strategies.

The E3 ubiquitin ligase RING finger protein 6 (RNF6) has been widely recognized for its role in promoting tumorigenesis in multiple cancers. However, we found that 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 (MS-MS) 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/phospho-Rb 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.