Gjb4 serves as a novel biomarker for lung cancer and promotes metastasis and chemoresistance via Src activation

Abstract

Most lung cancer patients are diagnosed late with metastasis, which is the major cause of cancer-related death and recurrent tumors that often exhibit chemoresistance. In the present study, we initially identified gap junction beta-4 protein (Gjb4) to be overexpressed in highly metastatic cancer cells selected by their enhanced binding to serum components. Overexpression or knockdown of Gjb4 increased or decreased lung metastasis of syngeneic mice, respectively. We found that Gjb4 expression was higher in lung tumors than normal tissues (p = 0.0026), and Gjb4 levels in blood buffy coat samples showed significant performance in diagnosing stage I-III (p = 0.002814) and stage IV (p < 0.0001) lung cancer. Moreover, high Gjb4 expression levels were correlated with poor prognosis (p = 1.4e-4) and recurrence (p = 1.9e-12). Using syngeneic mouse model, we observed that Gjb4 was able to promote tumor growth. High molecular weight serum fraction containing the major growth factor component IGF1 was able to induce Gjb4 via PKC pathway. Gjb4 activated Src signaling via MET, and overexpression of Gjb4 enhanced sphere-forming ability and anchorage-independent growth, which were reversed by inhibition of Src. In addition, we demonstrated that Gjb4-mediated Src activation enhanced chemoresistance of cancer cells toward gemcitabine and etoposide. The combination of Gjb4 knockdown, gemcitabine, and dasatinib further enhanced the inhibition of cancer cell viability. Together, our study has identified Gjb4 as a potential novel diagnostic and prognostic biomarker for lung cancer. Targeting Gjb4 may be exploited as a modality for improving lung cancer therapy.

Insight into the Role and Regulation of Gap Junction Genes in Lung Cancer and Identification of Nuclear Cx43 as a Putative Biomarker of Poor Prognosis

“…On the other hand, high Cx32 expression predicted better survival in overal NSCLC and LUAD patients, whereas LUSC patients had a tendency to perform worse if grouped in the cohort with high Cx32 expression (Figure 3b). The recent findings that Cx30.3 is linked to tumour progression [46] are strongly supported by our in silico analysis, which predicted significantly worse survival in the NSCLC group and the LUAD subtype (Figure 3c). Notably, other connexins (such as Cx31, known to be expressed in lung cancer) seemed to follow a similar pattern (Table 2).…”

“…Others have shown that GJIC-mediated transfer of small RNAs from lung cancer cells to astrocytes can alter cancer cell resistance to chemotherapy [45]. More recently, Cx30.3 was shown to be overexpressed in lung tumours and to be associated with poor prognosis and recurrence [46]. Functionally, Cx30.3 appears to activate the c-Src proto-oncogene to induce a number of cellular traits associated with malignancy.…”

Dasatinib reverses drug resistance by downregulating MDR1 and Survivin in Burkitt lymphoma cells

“…It has been indicated that dasatinib suppresses diffuse large B-cell lymphoma cell proliferation in vitro and tumor growth in vivo through inhibition of Src phosphorylation [29]. In addition, Src activation by gap junction beta-4-induced chemoresistance to gemcitabine and etoposide, in addition to dasatinib enhances the cytotoxic effect of gemcitabine in lung cancer [48]. It has been reported that dasatinib enhances the inhibitory effect of tumor cell growth by trametinib, a mitogenactivated protein kinase kinase inhibitor, in vitro and in vivo in various KRAS-mutant cancer cells, including lung, breast, colon, and pancreatic cancer cells [49].…”

Connexins in cancer: bridging the gap to the clinic

“…In lung cancer, the reduced expression of Cx43 mRNA in adjacent normal lung tissue (due to promoter methylation) is significantly correlated with nodal involvement, suggesting that Cx43 could be a marker for micrometastasis in non-small cell lung cancer [8]. Recently, Cx30.3 ( GJB4 ) mRNA expression was shown to be increased in lung tumours, with the levels in blood buffy coat samples serving as a biomarker for diagnosis and poor prognosis [67]. Mechanistically, Cx30.3 was shown to promote tumour growth and induce chemoresistance via the MET-induced activation of Src.…”