Hunk/Mak-v is a negative regulator of intestinal cell proliferation

Background: Conditional deletion of the tumour suppressor gene Apc within the murine intestine results in acute Wnt signalling activation. The associated over-expression of a myriad of Wnt signalling target genes yields phenotypic alterations that encompass many of the hallmarks of neoplasia. Previous transcriptomic analysis aimed at identifying genes that potentially play an important role in this process, inferred the Hormonally upregulated Neu-associated kinase (HUNK/Mak-v/Bstk1) gene as a possible candidate. Hunk is a SNF1 (sucrose non fermenting 1)-related serine/threonine kinase with a proposed association with many different tumour types, including colorectal cancer. Methods: Here we describe the generation of a novel Hunk kinase deficient mouse which has been used to investigate the involvement of Hunk-kinase activity in intestinal homeostasis and tumourigenesis. Results: We show that in the morphologically normal intestine, Hunk-kinase negatively regulates epithelial cell proliferation. However, the increase in cell proliferation observed in the Hunk kinase deficient intestine is counteracted by increased cell migration, thereby maintaining intestinal homeostasis. Using qRT-PCR, we further demonstrate that Hunk is significantly over-expressed in Apc deficient / Wnt-signalling activated intestinal tissue. Using the classical intestinal tumourigenesis Apc(Min) mouse model we show that loss of Hunk-kinase activity significantly reduced tumour initiation rates in the small intestine. However, an accompanying increase in the size of the tumours counteracts the impact this has on overall tumour burden or subsequently survival. Conclusions: In the intestinal setting we demonstrate that Hunk has a role in normal intestinal proliferation and homeostasis and, although it does not alter overall survival rates, activity of this kinase does impact on tumour initiation rates during the early stages in tumourigenesis in the small intestine.