Signaling adaptor protein Crk is involved in malignant feature of pancreatic cancer associated with phosphorylation of c-Met

Potential of targeting signal-transducing adaptor protein-2 in cancer therapeutic applications

Adaptor proteins play essential roles in various intracellular signaling pathways. Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that possesses pleckstrin homology (PH) and Src homology 2 (SH2) domains, as well as a YXXQ signal transducer and activator of transcription 3 (STAT3)-binding motif in its C-terminal region. STAP-2 is also a substrate of breast tumor kinase (BRK). STAP-2/BRK expression is deregulated in breast cancers and enhances STAT3-dependent cell proliferation. In prostate cancer cells, STAP-2 interacts with and stabilizes epidermal growth factor receptor (EGFR) after stimulation, resulting in the upregulation of EGFR signaling, which contributes to cancer-cell proliferation and tumor progression. Therefore, inhibition of the interaction between STAP-2 and BRK/EGFR may be a possible therapeutic strategy for these cancers. For this purpose, peptides that interfere with STAP-2/BRK/EGFR binding may have great potential. Indeed, the identified peptide inhibitor successfully suppressed the STAP-2/EGFR protein interaction, EGFR stabilization, and cancer-cell growth. Furthermore, the peptide inhibitor suppressed tumor formation in human prostate- and lung-cancer cell lines in a murine xenograft model. This review focuses on the inhibitory peptide as a promising candidate for the treatment of prostate and lung cancers.

A peptide derived from adaptor protein STAP-2 inhibits tumor progression by downregulating epidermal growth factor receptor signaling

Signal-transducing adaptor family member-2 (STAP-2) is an adaptor protein that regulates various intracellular signals. We previously demonstrated that STAP-2 binds to epidermal growth factor receptor (EGFR) and facilitates its stability and activation of EGFR signaling in prostate cancer cells. Inhibition of this interaction may be a promising direction for cancer treatment. Here, we found that 2D5 peptide, a STAP-2-derived peptide, blocked STAP-2-EGFR interactions and suppressed EGFR-mediated proliferation in several cancer cell lines. 2D5 peptide inhibited tumor growth of human prostate cancer cell line DU145 and human lung cancer cell line A549 in murine xenograft models. Additionally, we determined that EGFR signaling and its stability were decreased by 2D5 peptide treatment during EGF stimulation. In conclusion, our study shows that 2D5 peptide is a novel anticancer peptide that inhibits STAP-2-mediated activation of EGFR signaling and suppresses prostate and lung cancer progression.

MicroRNA-215-5p Inhibits the Proliferation and Migration of Wilm's Tumor Cells by Targeting CRK

Objective:

Wilm’s tumor is a common renal malignancy in childhood with unsatisfactory prognosis. microRNA-215-5p (miR-215-5p) has been reported as a tumor-suppressive miRNA in different types of human cancers, but rarely in the Wilm’s tumor. In light of this, we tried to investigate the regulatory role and underlying mechanism of miR-215-5p in the Wilm’s tumor.

Methods:

After sample collection and cell culture, the expression of miR-215-5p and CT10 Regulator of Kinase (CRK) was detected. Then rhabdoid tumor cell lines (formerly classified as Wilms’ tumor cell lines), G401 and WT-CLS1 cells were transfected with pcDNA3.1, pcDNA3.1-CRK, sh-NC, sh-CRK, agomir NC, miR-215-5p agomir, antagomir NC or miR-215-5p antagomir to explore the function of miR-215-5p and CRK in the Wilm’s tumor cell proliferation and migration. Moreover, the relationship between miR-215-5p and CRK was analyzed by dual luciferase reporter gene assay.

Results:

Lowly-expressed miR-215-5p and highly-expressed CRK were observed in the Wilm’s tumor tissues and cells. Transfection of pcDNA3.1-CRK or miR-215-5p antagomir could promote G401 and WT-CLS1 cell proliferation and enhance migration ability, while transfection of sh-CRK or miR-215-5p agomir led to opposite results. Additionally, miR-215-5p may bind to CRK. Moreover, transfection of pcDNA3.1-CRK in G401 and WT-CLS1 cells could partially reverse the inhibitory effect of miR-215-5p agomir on the proliferation and migration of Wilm’s tumor cells.

Conclusion:

Our study highlighted that miR-215-5p could suppress the proliferation and migration of Wilm’s tumor cells by regulating the expression of CRK, providing new ideas for molecular targeted therapy for Wilm’s tumor.

Crk and CrkL as Therapeutic Targets for Cancer Treatment

Crk and CrkL are cellular counterparts of the viral oncoprotein v-Crk. Crk and CrkL are overexpressed in many types of human cancer, correlating with poor prognosis. Furthermore, gene knockdown and knockout of Crk and CrkL in tumor cell lines suppress tumor cell functions, including cell proliferation, transformation, migration, invasion, epithelial-mesenchymal transition, resistance to chemotherapy drugs, and in vivo tumor growth and metastasis. Conversely, overexpression of tumor cells with Crk or CrkL enhances tumor cell functions. Therefore, Crk and CrkL have been proposed as therapeutic targets for cancer treatment. However, it is unclear whether Crk and CrkL make distinct or overlapping contributions to tumor cell functions in various cancer types because Crk or CrkL have been examined independently in most studies. Two recent studies using colorectal cancer and glioblastoma cells clearly demonstrated that Crk and CrkL need to be ablated individually and combined to understand distinct and overlapping roles of the two proteins in cancer. A comprehensive understanding of individual and overlapping roles of Crk and CrkL in tumor cell functions is necessary to develop effective therapeutic strategies. This review systematically discusses crucial functions of Crk and CrkL in tumor cell functions and provides new perspectives on targeting Crk and CrkL in cancer therapy.