Human MUC4 mucin induces ultra-structural changes and tumorigenicity in pancreatic cancer cells

MUC4 is a type- 1 transmembrane glycoprotein and is overexpressed in many carcinomas. It is a heterodimeric protein of 930 kDa, composed of a mucin- type subunit, MUC4 alpha, and a membrane- bound growth factor- like subunit, MUC4 beta. MUC4 mRNA contains unique 50 and 30 coding sequences along with a large variable number of tandem repeat ( VNTR) domain of 7 - 19 kb. A direct association of MUC4 overexpression has been established with the degree of invasiveness and poor prognosis of pancreatic cancer. To understand the precise role of MUC4 in pancreatic cancer, we engineered a MUC4 complementary DNA construct, mini- MUC4, whose deduced protein ( 320 kDa) is comparable with that of wild- type MUC4 ( 930 kDa) but represents only 10% of VNTR. Stable ectopic expression of mini- MUC4 in two human pancreatic cancer cell lines, Pancl and MiaPaCa, showed that MUC4 minigene expression follows a biosynthesis and localisation pattern similar to the wild- type MUC4. Expression of MUC4 resulted in increased growth, motility, and invasiveness of the pancreatic cancer cells in vitro. Ultra- structural examination of MUC4- transfected cells showed the presence of increased number and size of mitochondria. The MUC4- expressing cells also demonstrated an enhanced tumorigenicity in an orthotopic xenograft nude mice model, further supporting a direct role of MUC4 in inducing the cancer properties. In conclusion, our results suggest that MUC4 promotes tumorigenicity and is directly involved in growth and survival of the cancer cells.