HT-29 human colon cancer cell proliferation is regulated by cytosolic phospholipase A(2)α dependent PGE(2)via both PKA and PKB pathways.

Cytosolic phospholipase A(2)α (cPLA(2)α) up-regulation has been reported in human colorectal cancer cells, thus we aimed to elucidate its role in the proliferation of the human colorectal cancer cell line, HT-29. EGF caused a rapid activation of cPLA(2)α which coincided with a significant increase in cell proliferation. The inhibition of cPLA(2)α activity by pyrrophenone or by antisense oligonucleotide against cPLA(2)α (AS) or inhibition of prostaglandin E(2) (PGE(2)) production by indomethacin resulted with inhibition of cell proliferation, that was restored by addition of PGE(2). The secreted PGE(2) activated both protein kinase A (PKA) and PKB/Akt pathways via the EP2 and EP4 receptors. Either, the PKA inhibitor (H-89) or the PKB/Akt inhibitor (Ly294002) caused a partial inhibition of cell proliferation which was restored by PGE(2). But, inhibited proliferation in the presence of both inhibitors could not be restored by addition of PGE(2). AS or H-89, but not Ly294002, inhibited CREB activation, suggesting that CREB activation is mediated by PKA. AS or Ly294002, but not H-89, decreased PKB/Akt activation as well as the nuclear localization of β-catenin and cyclin D1 and increased the plasma membrane localization of β-catenin with E-cadherin, suggesting that these processes are regulated by the PKB pathway. Similarly, Caco-2 cells exhibited cPLA(2)α dependent proliferation via activation of both PKA and PKB/Akt pathways. In conclusion, our findings suggest that the regulation of HT-29 proliferation is mediated by cPLA(2)α-dependent PGE(2) production. PGE(2)via EP induces CREB phosphorylation by the PKA pathway and regulates β-catenin and cyclin D1 cellular localization by PKB/Akt pathway.