The HPV E7 oncoprotein promotes LIM and SH3 Domain Protein 1 (LASP1) transcription via the Rb/E2F1 signalling pathway in HPV-positive cervical cancer cells

Since its discovery in a metastatic lymph node in breast cancer patients, LIM and SH3 Domain Protein (LASP1) has been shown to be over-expressed in and promote the progression of various cancers. We recently demonstrated that LASP1 is highly expressed in human Papillomavirus positive (HPV+) cervical cancers where it promotes cell proliferation and invasion. Importantly, we showed that the HPV E7 oncoprotein increased LASP1 expression by downregulating the microRNA miR-203, which directly targets the LASP1 mRNA 3UTR. However, whether LASP1 is regulated by other mechanisms in HPV+ cervical cancers is unclear. Here, we demonstrate an additional mechanism by which HPV E7 regulates LASP1 transcription. Our data demonstrates an important the role for Rb/E2F1 signalling in promoting LASP1 expression in HPV+ cervical cancer cells. Mechanistically, E7-mediated Rb binding and degradation is required for E7-driven LASP1 promoter activity. Overexpression of Rb decreased LASP1 promoter activity, LASP1 mRNA expression and LASP1 protein levels, whereas E2F1 expression promoted LASP1 expression. Importantly, E2F1 directly bound to the LASP1 promoter region and the E2F1 binding sites are essential for LASP1 expression in HPV+ cervical cancer cells. Finally, we demonstrate that LASP1 can partially rescue the growth defects observed in E2F1 knockdown cervical cancer cells. Taken together, our data show that HPV E7 regulates LASP1 expression via the Rb/E2F1 signalling pathway. In combination with our previous work, our studies demonstrate that HPV E7 employs multiple mechanisms to drive LASP1 expression, reinforcing the importance of LASP1 in HPV+ cervical cancer.