PKCδ-mediated regulation of FLIP expression in human colon cancer cells

Abstract

FLICE-like inhibitory protein (FLIP), a naturally occurring caspase-inhibitory protein that lacks the critical cysteine domain necessary for catalytic activity, is a negative regulator of Fas-induced apoptosis. Decreased FLIP levels sensitize tumor cells to Fas-and TRAIL-mediated apoptosis; however, the cellular mechanisms regulating FLIP expression have not been defined. Here, we examined the roles of the PKC and NF-jB pathway in the regulation of FLIP in human colon cancers. FLIP mRNA levels were increased in Caco-2 cells by treatment with PMA; actinomycin D completely inhibited the induction of FLIP by PMA, indicating transcriptional regulation. PKC inhibitors G€ o6983 and Ro-31-8220 blocked PMA-stimulated FLIP expression. Pretreatment with the PKCdselective inhibitor rottlerin or transfection with PKCd siRNA inhibited PMA-induced FLIP expression, which identifies a role for PKCd in FLIP induction. Treatment with the proteasome inhibitor, MG132, or the NF-jB inhibitor (e.g., PDTC and gliotoxin), or overexpression of the superrepressor of IjB-a inhibited PMA-induced upregulation of FLIP. Moreover, PMA-induced NF-jB transactivation was blocked by GF109203x. In conclusion, our results demonstrate a critical role for PKCd/NF-jB in the regulation of FLIP in human colon cancer cells. ' 2005 Wiley-Liss, Inc.

Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

“…There is, however, at least one report that inhibition of this isoenzyme is sufficient to promote cell death (Lewis et al, 2005). Moreover, recent studies indicate that PKC-d can mediate antiapoptotic signals in some colon cancer cells (Wang et al, 2004(Wang et al, , 2006. Thus, PKC-d signaling can drive growth promotion or inhibition, and enhance or inhibit apoptosis in cell context-specific manners.…”

Downregulation of Bid is associated with PKCɛ-mediated TRAIL resistance

“…[8][9][10][11] Downregulation/mutations in caspase-8 or increased expression of FLIP can contribute to TRAIL resistance. 3,[12][13][14][15] The presence of antiapoptotic proteins, such as Akt or Bcl-2 family members can also contribute to TRAIL resistance by affecting either the extrinsic or the intrinsic cell death pathway. 2,10,[15][16][17][18] Protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinases, is emerging as a critical regulator of cellular responses to TRAIL.…”

“…2,10,[15][16][17][18] Protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinases, is emerging as a critical regulator of cellular responses to TRAIL. 12,14,[18][19][20][21][22][23][24] The PKC family consists of 11 isoforms that are classified as conventional (a, b1, b2 and g), novel (d, e, Z and y) or atypical (z and i/l). 25 PKCs are involved in the regulation of cell proliferation, differentiation as well as cell death.…”

“…20 PKC inhibitors inhibited FLIP and cIAP-2 expression in multiple myeloma cells. 12,14 In melanoma and breast cancer MCF-7 cells, PKC acted upstream of mitochondria but downstream of caspase-8 and Bid. 19,22 In the latter study, the effect of phorbol myristic acetate (PMA) was examined but the contribution of a specific PKC isoform was not tested.…”

“…The mechanism of TRAIL resistance may vary depending on the PKC isozyme. 14,18,19,24,31 PKCe has been implicated in inhibiting TRAIL-induced apoptosis in glioma and melanoma cells. 18,19,23 Increased levels and activity of PKCe were associated with TRAIL resistance, 19 and overexpression of PKCe inhibited TRAILinduced apoptosis in these cells.…”