Old Habits Die Hard: Addiction of BRAF-Mutant Cancer Cells to MAP Kinase Signaling

Ring finger protein 215 is a potential prognostic biomarker involved in immune infiltration and angiogenesis in colorectal cancer

The prognostic value of ring finger protein 215 (RNF215) in colorectal cancer (CRC) is unclear. Herein, the present study aimed to investigate the precise value of RNF215 based on CRC datasets from The Cancer Genome Atlas (TCGA) and clinical cases. CRC patient data was collected from TCGA and clinical samples from the Department of Pathology, Shanghai Fifth People's Hospital, Fudan University (Shanghai, China). Logistic regression analysis was used to investigate the correlations between RNF215 and clinicopathological characteristics. The predictive value of RNF215 for the clinical outcome of CRC was determined using Kaplan-Meier curves and Cox regression. Gene set enrichment analysis (GSEA), single-sample GSEA (ssGSEA), and angiogenesis analysis were also conducted to investigate the biological role of RNF215. Immunohistochemistry was conducted to validate the results. The results of the present study confirmed that RNF215 protein expression was significantly associated with age, lymphatic invasion, and overall survival (OS). Univariate analysis showed that upregulation of RNF215 in CRC was significantly associated with age and lymphatic invasion. Kaplan-Meier survival analysis revealed that high RNF215 expression predicted poorer OS and disease-specific survival. A total of nine experimentally detected RNF215-binding proteins were identified with the STRING tool and Cytoscape software. GSEA suggested that RNF215 was associated with several important pathways involved in tumor occurrence, including the Kyoto Encyclopedia of Genes and Genomes MAPK signaling pathway and the WikiPathway RAS signaling pathway. ssGSEA confirmed that RNF215 was significantly expressed in natural killer cells, CD8 T cells and T helper cells. Angiogenesis analysis revealed that numerous angiogenesis-related genes had the same expression trend as RNF215 in CRC. The immunostaining results indicated that RNF215 expression was significantly higher in CRC tissues than in corresponding normal tissues. In conclusion, increased RNF215 expression may be a potential molecular marker predictive of poor survival and a treatment target in CRC. In addition, RNF215 may participate in the formation of CRC through a variety of signaling pathways.

Mitogen-induced transcriptional programming in human fibroblasts

Treatment of serum-starved quiescent human cells with fetal bovine serum (FBS), epidermal growth factor (EGF), or the phorbol ester (12-O-tetradecanoylphorbol-13-acetate, TPA) activates the RAS-MAPK pathway which initiates a transcriptional program which drives cells toward proliferation. Stimulation of the RAS-MAPK pathway activates mitogen- and stress-activated kinases (MSK) 1 and 2, which phosphorylate histone H3 at S10 (H3S10ph) or S28 (H3S28ph) (nucleosomal response) located at the regulatory regions of immediate-early genes, setting in motion a series of chromatin remodeling events that result in transcription initiation. To investigate immediate-early genes regulated by the MSK, we have completed transcriptome analyses (RNA sequencing) of human normal fibroblast cells (CCD-1070Sk) stimulated with EGF or TPA ± H89, a potent MSK/PKA inhibitor. The induction of many immediate-early genes was independent of MSK activity. However, the induction of immediate-early genes attenuated with H89 also had reduced induction with the PKA inhibitor, Rp-cAMPS. Several EGF-induced genes, coding for transcriptional repressors, were further upregulated with H89 but not with Rp-cAMPS, suggesting a role for MSK in modulating the induction level of these genes.

Autocrine/paracrine actions of growth hormone in human melanoma cell lines

Melanoma is the most aggressive skin cancer. Its aggressiveness is most commonly attributed to ERK pathway mutations leading to constitutive signaling. Though initial tumor regression results from targeting this pathway, resistance often emerges. Interestingly, interrogation of the NCI-60 database indicates high growth hormone receptor (GHR) expression in melanoma cell lines. To further characterize melanoma, we tested responsiveness to human growth hormone (GH). GH treatment resulted in GHR signaling and increased invasion and migration, which was inhibited by a GHR monoclonal antibody (mAb) antagonist in WM35, SK-MEL 5, SK-MEL 28 and SK-MEL 119 cell lines. We also detected GH in the conditioned medium (CM) of human melanoma cell lines. GHR, JAK2 and STAT5 were basally phosphorylated in these cell lines, consistent with autocrine/paracrine GH production. Together, our results suggest that melanomas are enriched in GHR and produce GH that acts in an autocrine/paracrine manner. We suggest that GHR may constitute a therapeutic target in melanoma.

MEK Inhibition Modulates Cytokine Response to Mediate Therapeutic Efficacy in Lung Cancer

Activating mutations in BRAF, a key mediator of RAS signaling, are present in approximately 50% of melanoma patients. Pharmacologic inhibition of BRAF or the downstream MAP kinase MEK is highly effective in treating BRAF-mutant melanoma. In contrast, RAS pathway inhibitors have been less effective in treating epithelial malignancies, such as lung cancer. Here, we show that treatment of melanoma patients with BRAF and MEK inhibitors (MEKi) activated tumor NF-κB activity. MEKi potentiated the response to TNFα, a potent activator of NF-κB. In both melanoma and lung cancer cells, MEKi increased cell-surface expression of TNFα receptor 1 (TNFR1), which enhanced NF-κB activation and augmented expression of genes regulated by TNFα and IFNγ. Screening of 289 targeted agents for the ability to increase TNFα and IFNγ target gene expression demonstrated that this was a general activity of inhibitors of MEK and ERK kinases. Treatment with MEKi led to acquisition of a novel vulnerability to TNFα and IFNγ-induced apoptosis in lung cancer cells that were refractory to MEKi killing and augmented cell-cycle arrest. Abolishing the expression of TNFR1 on lung cancer cells impaired the antitumor efficacy of MEKi, whereas the administration of TNFα and IFNγ in MEKi-treated mice enhanced the antitumor response. Furthermore, immunotherapeutics known to induce expression of these cytokines synergized with MEKi in eradicating tumors. These findings define a novel cytokine response modulatory function of MEKi that can be therapeutically exploited. SIGNIFICANCE: Lung cancer cells are rendered sensitive to MEK inhibitors by TNFα and IFNγ, providing a strong mechanistic rationale for combining immunotherapeutics, such as checkpoint blockers, with MEK inhibitor therapy for lung cancer.See related commentary by Havel, p. 5699.

Mitogen and stress- activated protein kinase regulated gene expression in cancer cells

The mitogen- and stress-activated protein kinases activated by the extracellular-signal-regulated kinase 1/2 and/or stress-activated protein kinase 2/p38 mitogen-activated protein kinase pathways are recruited to the regulatory region of a subset of genes termed immediate-early genes, often leading to their induction. These genes, many of which code for transcription factors, have been directly linked to the phenotypic events in carcinogenesis. In this paper, we focus on the mitogen- and stress-activated protein kinases; their discovery, activation, H3 phosphorylation and recent discoveries in their roles in cancer.

PRIMA-1Met suppresses colorectal cancer independent of p53 by targeting MEK

PRIMA-1^Met is the methylated PRIMA-1 (p53 reactivation and induction of massive apoptosis) and could restore tumor suppressor function of mutant p53 and induce p53 dependent apoptosis in cancer cells harboring mutant p53. However, p53 independent activity of PRIMA-1^Met remains elusive. Here we reported that PRIMA-1^Met attenuated colorectal cancer cell growth irrespective of p53 status. Kinase profiling revealed that mitogen-activated or extracellular signal-related protein kinase (MEK) might be a potential target of PRIMA-1^Met. Pull-down binding and ATP competitive assay showed that PRIMA-1^Met directly bound MEK in vitro and in cells. Furthermore, the direct binding sites of PRIMA-1^Met were explored by using a computational docking model. Treatment of colorectal cancer cells with PRIMA-1^Met inhibited p53-independent phosphorylation of MEK, which in turn impaired anchorage-independent cell growth in vitro. Moreover, PRIMA-1^Met suppressed colorectal cancer growth in xenograft mouse model by inhibiting MEK1 activity.

Taken together, our findings demonstrate a novel p53-independent activity of PRIMA-1^Met to inhibit MEK and suppress colorectal cancer growth.

Biomarker Accessible and Chemically Addressable Mechanistic Subtypes of BRAF Melanoma

Genomic diversity among melanoma tumors limits durable control with conventional and targeted therapies. Nevertheless, pathologic activation of the ERK1/2 pathway is a linchpin tumorigenic mechanism associated with the majority of primary and recurrent disease. Therefore, we sought to identify therapeutic targets that are selectively required for tumorigenicity in the presence of pathologic ERK1/2 signaling. By integration of multigenome chemical and genetic screens, recurrent architectural variants in melanoma tumor genomes, and patient outcome data, we identified two mechanistic subtypes of BRAF^V600 melanoma that inform new cancer cell biology and offer new therapeutic opportunities. Subtype membership defines sensitivity to clinical MEK inhibitors versus TBK1/IKBKε inhibitors. Importantly, subtype membership can be predicted using a robust quantitative five-feature genetic biomarker. This biomarker, and the mechanistic relationships linked to it, can identify a cohort of best responders to clinical MEK inhibitors and identify a cohort of TBK1/IKBKε inhibitor-sensitive disease among nonresponders to current targeted therapy.Significance: This study identified two mechanistic subtypes of melanoma: (1) the best responders to clinical BRAF/MEK inhibitors (25%) and (2) nonresponders due to primary resistance mechanisms (9.9%). We identified robust biomarkers that can detect these subtypes in patient samples and predict clinical outcome. TBK1/IKBKε inhibitors were selectively toxic to drug-resistant melanoma. Cancer Discov; 7(8); 832-51. ©2017 AACR.See related commentary by Jenkins and Barbie, p. 799This article is highlighted in the In This Issue feature, p. 783.