c-CBL regulates melanoma proliferation, migration, invasion and the FAK-SRC-GRB2 nexus

The role of CBL family ubiquitin ligases in cancer progression and therapeutic strategies

The CBL (Casitas B-lineage lymphoma) family, as a class of ubiquitin ligases, can regulate signal transduction and activate receptor tyrosine kinases through various tyrosine kinase-dependent pathways. There are three members of the family: c-CBL, CBL-b, and CBL-c. Numerous studies have demonstrated the important role of CBL in various cellular pathways, particularly those involved in the occurrence and progression of cancer, hematopoietic development, and regulation of T cell receptors. Therefore, the purpose of this review is to comprehensively summarize the function and regulatory role of CBL family proteins in different human tumors, as well as the progress of drug research targeting CBL family, so as to provide a broader clinical measurement strategy for the treatment of tumors.

C1632 inhibits ovarian cancer cell growth and migration by inhibiting LIN28 B/let-7/FAK signaling pathway and FAK phosphorylation

The highly conserved RNA-binding protein LIN28B and focal adhesion kinase (FAK) are significantly upregulated in ovarian cancer (OC), serving as markers for disease progression and prognosis. Nonetheless, the correlation between LIN28B and FAK, as well as the pharmacological effects of the LIN28 inhibitor C1632, in OC cells have not been elucidated. The present study demonstrates that C1632 significantly reduced the rate of DNA replication, arrested the cell cycle at the G0/G1 phase, consequently reducing cell viability, and impeding clone formation. Moreover, treatment with C1632 decreased cell-matrix adhesion, as well as inhibited cell migration and invasion. Further mechanistic studies revealed that C1632 inhibited the OC cell proliferation and migration by concurrently inhibiting LIN28 B/let-7/FAK signaling pathway and FAK phosphorylation. Furthermore, C1632 exhibited an obvious inhibitory effect on OC cell xenograft tumors in mice. Altogether, these findings identified that LIN28 B/let-7/FAK is a valuable target in OC and C1632 is a promising onco-therapeutic agent for OC treatment.

Oncogenic signaling pathways and hallmarks of cancer in Korean patients with acral melanoma

Acral melanoma (AM), a rare subtype of cutaneous melanoma, shows higher incidence in Asians, including Koreans, than in Caucasians. However, the genetic modification associated with AM in Koreans is not well known and has not been comprehensively investigated in terms of oncogenic signaling, and hallmarks of cancer. We performed whole-exome and RNA sequencing for Korean patients with AM and acquired the genetic alterations and gene expression profiles. KIT alterations (previously known to be recurrent alterations in AM) and CDK4/CCND1 copy number amplifications were identified in the patients. Genetic and transcriptomic alterations in patients with AM were functionally converge to the hallmarks of cancer and oncogenic pathways, including 'proliferative signal persistence', 'apoptotic resistance', and 'activation of invasion and metastasis', despite the heterogeneous somatic mutation profiles of Korean patients with AM. This study may provide a molecular understanding for therapeutic strategy for AM.

Atrazine modifies markers of melanocyte maturation and apoptosis in primary skin cultures

Atrazine (ATZ) is part of a group of herbicides called triazines. ATZ is widely used in agricultural areas of Mexico, commonly used for the selective control of weeds in corn and sorghum crops. The exposure to ATZ can have serious human health effects since its use was associated with the development of cutaneous melanoma in an epidemiological study. The aim of this study was to evaluate the expression of maturation and apoptotic markers in primary skin cultures exposed to ATZ. The primary skin cultures were exposed to 0.1, and 10 µM ATZ with or without ultraviolet (UV) radiation and the expression of maturation and apoptotic markers were evaluated by RT-qPCR. We observed a significant increase in all the melanocyte maturation markers in cells exposed to ATZ with or without UV, with SOX-9 and FAK (melanoblast markers) being the highest. Also, the expression of BCL-2 (anti-apoptotic marker) was the most increased gene in cells exposed to ATZ with or without UV. Low concentrations of ATZ and UV radiation induce genetic changes associated with the development of immature melanocytes and activate mechanisms associated with the inhibition of apoptosis characteristics of malignant cell transformation, which will allow proposing new therapeutic targets and generating new restrictions or care in farmers exposed to pesticides such as the ATZ.

Pro-prion, as a membrane adaptor protein for E3 ligase c-Cbl, facilitates the ubiquitination of IGF-1R, promoting melanoma metastasis

Aberrant activation of receptor tyrosine kinase (RTK) is usually a result of mutation and plays important roles in tumorigenesis. How RTK without mutation affects tumorigenesis remains incompletely understood. Here we show that in human melanomas pro-prion (pro-PrP) is an adaptor protein for an E3 ligase c-Cbl, enabling it to polyubiquitinate activated insulin-like growth factor-1 receptor (IGF-1R), leading to enhanced melanoma metastasis. All human melanoma cell lines studied here express pro-PrP, retaining its glycosylphosphatidylinositol-peptide signal sequence (GPI-PSS). The sequence, PVILLISFLI in the GPI-PSS of pro-PrP, binds c-Cbl, docking c-Cbl to the inner cell membrane, forming a pro-PrP/c-Cbl/IGF-1R trimeric complex. Subsequently, IGF-1R polyubiquitination and degradation are augmented, which increases autophagy and tumor metastasis. Importantly, the synthetic peptide PVILLISFLI disrupts the pro-PrP/c-Cbl/IGF-1R complex, reducing cancer cell autophagy and mitigating tumor aggressiveness in vitro and in vivo. Targeting cancer-associated GPI-PSS may provide a therapeutic approach for treating human cancers expressing pro-PrP.

The AhR-SRC axis as a therapeutic vulnerability in BRAFi-resistant melanoma

The nongenetic mechanisms required to control tumor phenotypic plasticity and shape drug-resistance remain unclear. We show here that the Aryl hydrocarbon Receptor (AhR) transcription factor directly regulates the gene expression program associated with the acquisition of resistance to BRAF inhibitor (BRAFi) in melanoma. In addition, we show in melanoma cells that canonical activation of AhR mediates the activation of the SRC pathway and promotes the acquisition of an invasive and aggressive resistant phenotype to front-line BRAFi treatment in melanoma. This nongenetic reprogramming identifies a clinically compatible approach to reverse BRAFi resistance in melanoma. Using a preclinical BRAFi-resistant PDX melanoma model, we demonstrate that SRC inhibition with dasatinib significantly re-sensitizes melanoma cells to BRAFi. Together we identify the AhR/SRC axis as a new therapeutic vulnerability to trigger resistance and warrant the introduction of SRC inhibitors during the course of the treatment in combination with front-line therapeutics to delay BRAFi resistance.

Four Immune Modulating Genes in Primary Melanoma That Predict Metastatic Potential

INTRODUCTION

Histologic characteristics cannot adequately predict which patients are at risk of developing metastatic disease after excision of primary cutaneous melanoma. The aim of this study was to identify immunomodulatory genes in primary tumors associated with development of distant metastases.

MATERIALS AND METHODS

Thirty-seven patients with primary melanoma underwent surgical excision. RNA was extracted from the primary tumor specimens. cDNA was synthesized and used with Human Gene Expression microarray. Differential expression of 74 immunomodulatory genes was compared between patients who developed distant metastases and those who did not.

RESULTS

Six of 37 patients developed distant metastases during the time of the study. Differential expression of microarray data showed upregulation of four immunomodulatory genes in this group. These four genes-c-CBL, CD276, CXCL1, and CXCL2-were all significantly overexpressed in the metastatic group with differential expression fold change of 1.15 (P = 0.01), 1.16 (P = 0.04), 2.51 (P < 0.001), and 1.68 (P < 0.02), respectively. CXCL1 had particularly high predictive value with an area under the curve of 0.80. Multivariate analysis showed only expression of CXCL1 (P = 0.01) remains predictive of distant metastases in melanoma patients. This result was confirmed using quantitative real-time polymerase chain reaction.

CONCLUSIONS

CXCL1, CXCL2, c-CBL, and CD276 are immunomodulatory genes present in primary melanoma that are strongly associated with development of metastatic disease. Identification of their presence, particularly CXCL1, in the primary tumor could be used as a predictor of future risk of metastatic disease and thereby to identify patients who might benefit early from immunotherapy.

An Update on the Role of Ubiquitination in Melanoma Development and Therapies

The ubiquitination system plays a critical role in regulation of large array of biological processes and its alteration has been involved in the pathogenesis of cancers, among them cutaneous melanoma, which is responsible for the most deaths from skin cancers. Over the last decades, targeted therapies and immunotherapies became the standard therapeutic strategies for advanced melanomas. However, despite these breakthroughs, the prognosis of metastatic melanoma patients remains unoptimistic, mainly due to intrinsic or acquired resistances. Many avenues of research have been investigated to find new therapeutic targets for improving patient outcomes. Because of the pleiotropic functions of ubiquitination, and because each step of ubiquitination is amenable to pharmacological targeting, much attention has been paid to the role of this process in melanoma development and resistance to therapies. In this review, we summarize the latest data on ubiquitination and discuss the possible impacts on melanoma treatments.

E3 ligase-inactivation rewires CBL interactome to elicit oncogenesis by hijacking RTK-CBL-CIN85 axis

Casitas B-lineage lymphoma (CBL) is a ubiquitin ligase (E3) that becomes activated upon Tyr371-phosphorylation and targets receptor protein tyrosine kinases for ubiquitin-mediated degradation. Deregulation of CBL and its E3 activity is observed in myeloproliferative neoplasms and other cancers, including breast, colon, and prostate cancer. Here, we explore the oncogenic mechanism of E3-inactive CBL mutants identified in myeloproliferative neoplasms. We show that these mutants bind strongly to CIN85 under normal growth conditions and alter the CBL interactome. Lack of E3 activity deregulates CIN85 endosomal trafficking, leading to an altered transcriptome that amplifies signaling events to promote oncogenesis. Disruption of CBL mutant interactions with EGFR or CIN85 reduces oncogenic transformation. Given the importance of the CBL-CIN85 interaction in breast cancers, we examined the expression levels of CIN85, CBL, and the status of Tyr371-phosphorylated CBL (pCBL) in human breast cancer tissue microarrays. Interestingly, pCBL shows an inverse correlation with both CIN85 and CBL, suggesting that high expression of inactivated CBL could coordinate with CIN85 for breast cancer progression. Inhibition of the CBL-CIN85 interaction with a proline-rich peptide of CBL that binds CIN85 reduced the proliferation of MDA-MB-231 cells. Together, these results provide a rationale for exploring the potential of targeting the EGFR-CBL-CIN85 axis in CBL-inactivated mutant cancers.

miRNA-122-5p stimulates the proliferation and DNA synthesis and inhibits the early apoptosis of human spermatogonial stem cells by targeting CBL and competing with lncRNA CASC7

Epigenetic regulators of human spermatogonia stem cells (SSCs) remain largely unknown. We found that miRNA-122-5p was upregulated in human spermatogonia from obstructive azoospermia (OA) patients compared with non-obstructive azoospermia (NOA). MiRNA-122-5p stimulated the proliferation and DNA synthesis of human SSCs, whereas it inhibited the early apoptosis of human SSCs. CBL was predicted and identified as a direct target of miRNA-122-5p in human SSCs. CBL silencing led to an enhancement of cell proliferation and DNA synthesis and neutralized the effect of miRNA-122-5p inhibitor on the DNA synthesis of human SSCs. The decrease in the early apoptosis of human SSCs was observed after CBL knockdown. By comparing the profiles of lncRNAs between OA and NOA spermatogonia, CASC7 was significantly deficient in OA spermatogonia, and it had a direct association with miRNA-122-5p. LncRNA CASC7 competed with miRNA-122-5p, and it suppressed the inhibition of CBL. Collectively, these results implicate that miRNA-122-5p enhances the proliferation and DNA synthesis and inhibits the early apoptosis of human SSCs by targeting CBL and competing with lncRNA CASC7. Therefore, this study provides novel insights into epigenetic regulation of fate determinations of human SSCs, and it offers new targets for gene therapy of male infertility that is associated with aging.

Loss of c-Cbl expression correlates with de-differentiation status and lymphatic metastasis in gastric cancer

Context

C-Cbl is an important negative regulator of the cell signaling that acts as an adaptor protein and E3 ubiquitin ligase. The role of c-Cbl in development and regulation of human cancer has aroused intensive attention.

Aims

In this study, we aimed to assess the correlation between the expression of c-Cbl and clinicopathological parameters and explored the role of c-Cbl in the development and progression of GC.

Settings and Design

This is a Pilot study.

Methods and Materials

In total, 84 tissue samples including 44 gastric cancers (GC) and 40 matched adjacent normal tissues were collected after surgery. Then tissue microarray (TMA) and immunohistochemistry (IHC) technology were combined to detect the protein expression of c-Cbl.

Statistical Analysis Used

Statistical analysis was performed using SPSS 22.0 (IBM Corporation, Armonk, NY, USA).

Results

We have studied the correlation between c-Cbl expression and clinicopathological parameters. Our study showed that c-Cbl has a low expression in 61.4% (27/44) of GC tissues, and the incidence of cases was significantly higher than that in adjacent normal tissues (P < 0.0001). In addition, the correlation between c-Cbl expression and gastric carcinoma subtype (P = 0.027), histological type (P = 0.033), Borrmann classification (P = 0.009), histological differentiation (P = 0.0005), lymph node metastasis (P = 0.007), and intravascular tumor thrombus (P = 0.036) has also been revealed.

Conclusions

Our results show that c-Cbl is down-regulated in GC tissues compared with normal gastric tissue, which may play an important role in the development and progression of GC.

MicroRNA-133b/EGFR axis regulates esophageal squamous cell carcinoma metastases by suppressing anoikis resistance and anchorage-independent growth

Background

Anoikis resistance has been demonstrated to facilitate distant metastases of cancers. MicroRNA-133b (miR-133b) is found to be down-regulated in various tumors, including esophageal squamous cell carcinoma (ESCC), and closely correlates with the malignant phenotype of ESCC. This study aimed to evaluate the roles of miR-133b in metastases of ESCC via regulating anoikis.

Methods

The expression of miR-133b and related molecules were detected in ESCC tissues and cells. The target relationship between miR-133b and epidermal growth factor receptor (EGFR) was verified by dual luciferase reporter assay. Cell proliferation was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Anoikis and anchorage-independent growth were assessed by anoikis assay and soft agar assay. Migration and invasion were evaluated by scratch and transwell assays. The expressions of related molecules were detected by reverse transcription-quantitative polymerase chain reaction and western blotting. The in vivo results were determined by tumor xenografts in nude mice.

Results

MiR-133b level was decreased in ESCC tissues and cells, which negatively correlated with EGFR, integrin β4 (ITGB4), and phosphorylated focal adhesion kinase levels. Moreover, miR-133b down-regulated EGFR expression in ESCC cells. Overexpression of miR-133b inhibited the anoikis resistance, migration, invasion and epithelial-mesenchymal transition of ESCC cells via targeting EGFR. Finally, miR-133b overexpression suppressed tumor growth and lung metastases of ESCC in vivo. ITGB4/FAK/growth factor receptor-bound protein 2 (Grb2), protein kinase B (AKT), and extracellular signal-regulated kinase (ERK) pathways were involved in the regulatory mechanisms of miR-133b/EGFR axis in ESCC metastases in vitro and in vivo.

Conclusions

The results suggested that miR-133b/EGFR axis regulated metastases of ESCC by affecting anoikis resistance via ITGB4/FAK/Grb2, AKT, and ERK pathways.

Phycocyanin Reduces Proliferation of Melanoma Cells through Downregulating GRB2/ERK Signaling

As a type of functional food additive, phycocyanin is shown to have a potential antineoplastic property. However, its underlying anticancer mechanism in melanoma cells remains unknown. We previously reported a 35S in vivo/vitro labeling analysis for dynamic proteomic (SiLAD) technology. It could exclusively detect protein synthesis rates via pulse labeling of newly expressed proteins by 35S, providing a high time-resolution method for analysis of protein variations. In the present study, we performed a time course analysis in A375 melanoma cells after phycocyanin treatment using SiLAD. Protein expression velocities were specifically visualized and their regulation modes were dynamically traced. Strikingly, novel protein synthesis patterns were discovered in the early phase of phycocyanin treatment, suggesting a possible mechanism of phycocyanin regulation. Furthermore, network analysis and phenotype experiments demonstrated that GRB2-ERK1/2 pathway was involved in phycocyanin-mediated regulation process and responsible for the proliferation suppression of melanoma cell, which could be a therapeutic target for malignant melanoma.

Targeted Tumor Therapy Remixed-An Update on the Use of Small-Molecule Drugs in Combination Therapies

Over the last decade, the treatment of tumor patients has been revolutionized by the highly successful introduction of novel targeted therapies, in particular small-molecule kinase inhibitors and monoclonal antibodies, as well as by immunotherapies. Depending on the mutational status, BRAF and MEK inhibitor combinations or immune checkpoint inhibitors are current first-line treatments for metastatic melanoma. However, despite great improvements of survival rates limitations due to tumor heterogeneity, primary and acquired therapy resistance, immune evasion, and economical considerations will need to be overcome. Accordingly, ongoing clinical trials explore the individualized use of small-molecule drugs in new targeted therapy combinations based on patient parameters and tumor biopsies. With focus on melanoma therapy this review aims at providing a comprehensive overview of such novel alternative and combinational therapy strategies currently emerging from basic research. The molecular principles and drug classes that may hold promise for improved tumor therapy combination regimens including kinase inhibition, induction of apoptosis, DNA-damage response inhibition, epigenetic reprogramming, telomerase inhibition, redox modulation, metabolic reprogramming, proteasome inhibition, cancer stem cell transdifferentiation, immune cell signaling modulation, and others, are explained in brief. In addition, relevant targeted therapy combinations in current clinical trials and individualized treatment strategies are highlighted.

Refinement of the endogenous epitope tagging technology allows the identification of a novel NRAS binding partner in melanoma

The NRAS oncoprotein is highly mutated in melanoma. However, to date, no comprehensive proteomic study has been reported for NRAS. Here, we utilized the endogenous epitope tagging (EET) approach for the identification of novel NRAS binding partners. Using EET, an epitope tag is added to the endogenously expressed protein, via modification of its genomic coding sequence. Existing EET systems are not robust, suffer from high background, and are labor-intensive. To this end, we present a polyadenylation signal-trap construct for N'-tagging that generates a polycistronic mRNA with the gene of interest. This system requires the integration of the tagging cassette in frame with the target gene to be expressed. Using this design, we demonstrate, for the first time, endogenous tagging of NRAS in melanoma cells allowing the identification of the E3 ubiquitin ligase c-CBL as a novel NRAS binding partner. Thus, our developed EET technology allows the characterization of new RAS effectors, which could be beneficial for the design of future drugs that inhibit constitutive signaling of RAS oncogenic mutants.