SH3GL1 inhibition reverses multidrug resistance in colorectal cancer cells by downregulation of MDR1/P-glycoprotein via EGFR/ERK/AP-1 pathway

Multidrug resistance is one of the major reasons colorectal cancer (CRC) chemotherapy-based treatments fail, and novel biologically based therapies are urgently needed. Src homology 3 (SH3)-domain GRB2-like protein 1 (SH3GL1) is a membrane-bound protein which was found to be involved in tumor formation, progression, and metastasis. In this study, immunohistochemistry staining, quantitative real-time polymerase chain reaction (qRT-PCR), and western blot analysis revealed a high expression of SH3GL1 in human CRC tumor specimens and several CRC cells resistant to chemotherapeutics. Cell Counting Kit-8 (CCK-8) assay showed that transfection of pCDNA3.1(+)-SH3GL1 increased while transfection of SH3GL1 siRNA decreased cell viability in response to 5-fluorouracil (5-FU) treatment (P < 0.05). Further studies indicated that transfection of SH3GL1 siRNA significantly downregulated multidrug resistance protein 1 (MDR1)/P-glycoprotein expression (P < 0.05), decreased MDR1 promoter activity and activator protein-1 (AP-1) binding activity (P < 0.05), and inhibited the activation of epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinases 1/2 (ERK1/2) signaling (P < 0.05) in CRC cells resistant to chemotherapeutics. Transfection of pCDNA3.1(+)-SH3GL1 caused the opposite effect. Additionally, pre-treatment with either EGFR kinase inhibitor PD153035 or ERK1/2 kinase inhibitor PD98059 in HCT116/5-FU cells partly inhibits P-glycoprotein expression and AP-1 binding activity (P < 0.05). In conclusion, we confirmed that inhibition of SH3GL1 reverses multidrug resistance through declining P-glycoprotein expression via the EGFR/ERK/AP-1 pathway.