Regulation of MINK1 by APC, PKA and MARK3/4 and consequences for epithelial cell biology

Abstract

Colorectal cancer is the third most common cause of cancer-related deaths in the developed world. In most colorectal cancers the tumour suppressor gene adenomatous polyposis coli (APC) is mutated. The APC protein is closely linked to epithelial tissue homeostasis, it is a scaffolding protein in Wnt signalling and is important for cytoskeletal regulation. Misshapen/NIK-related kinase 1 (MINK1) was identified as a Wnt signalling independent interaction partner of APC and MINK1 is negatively regulated by APC in an evolutionary conserved process.

In my project, I investigated the biological function of MINK1, with the overall aim to identify how MINK1 might contribute to the cancer phenotype induced by APC mutations. Investigating the molecular association between APC and MINK1, I found that the linker domain of MINK1 and the N-terminal part of APC are required. Moreover, I confirmed that MINK1 phosphorylates ERM proteins on their activating phosphosite in vitro. My finding that MINK1 kinase activity was markedly reduced when the threonine ERM activating phosphosite was mutated to a serine suggested that MINK1 may be a threonine-selective kinase. I demonstrated that PKA, MARK3 and MARK4 directly phosphorylate MINK1 on two phosphosites (S674 and S701) in the linker domain of MINK1, which in turn enables 14-3-3-binding to MINK1. ERM proteins play an essential role in mitotic spindle formation, orientation and function and in cell migration. APC, too, has been linked to spindle orientation and MINK1 is phosphorylated during mitosis. Investigating the functional link suggested by these observations, I found that MINK1 overexpression caused spindle misorientation. So far, I was unable to show an essential role of MINK1 phosphorylation and activation of ERM proteins in vivo. The ability of MINK1 to phosphorylate ERM proteins at their activating phosphosite and the role of ERM proteins in cell migration, together with previously demonstrated roles of APC and MINK1 in cell migration, led to the hypothesis that MINK1 contributes to migration defects observed in APC mutant cells. I found that overexpression of MINK1 accelerated cell migration and likely contributes to area size of coordinated cell movement in collective migration. The exact mechanism behind these functions of MINK1 and its potential contribution to colorectal cancer caused by APC mutation will need further investigation.

Date of Award	2021
Original language	English
Awarding Institution	University of Dundee
Sponsors	Wellcome Trust
Supervisor	Inke Nathke (Supervisor), Carol MacKintosh (Supervisor) & Rastko Sknepnek (Supervisor)