Phorbol esters such as
phorbol 12-myristate 13-acetate (PMA) have been reported to modulate diverse cellular responses through signal transduction pathways including the
protein kinase C (PKC) pathway. In the present study, we sought to determine the effect of PMA on
mucin gene expression and on the
biological properties of a human
colon cancer cell line, HM3. The cells were treated for 8 and 24 h with various concentrations of PMA and total
RNA was extracted and Northern and slot blot analyses were carried out using MUC2, MUC3 and MUC5AC
mucin cDNA probes to assess the steady state levels of
mRNA. Spent media were collected and the level of
cancer associated carbohydrate antigens (T, Tn, sialyl Tn,
sialyl Lex, and sialyl Lea) and matrix-degrading
metalloproteinase (
MMPs) activity were examined. Trypsinized cells were used for assessing in vitro invasion, motility and adhesion to
matrigel. Our results showed that PMA caused upregulation of steady state
mRNA levels of MUC2, MUC3 and MUC5AC which was inhibited
after treatment with
protein synthesis inhibitors.
Calphostin C, a highly specific inhibitor of
protein kinase C significantly inhibited the PMA induced induction of
mRNA levels of MUC2, MUC3, and MUC5AC. The levels of all
cancer-associated
mucin carbohydrate antigens examined in the media were increased by PMA treatment. PMA also caused an increase in
MMPs activity and in in vitro invasion and motility properties, but did not affect adhesion of HM3 cells to
matrigel. Thus, PMA caused a significant increase in the expression of all three
mucin genes through signaling pathways involving
protein kinase C and increased secretion of
mucin associated
carbohydrate antigens. These changes were associated with increases in
MMP activity as well as by increases in the invasive and motility properties of HM3
colon cancer cells. These data suggest that
protein kinase C signaling pathways may be involved in
mucin gene regulation and in modulating the invasive and metastatic properties of
colon cancer cells.