Conventional protein kinase C plays a critical role in negative regulation of CD98‐induced homotypic aggregation

Abstract

CD98, a heterodimeric type II transmembrane protein, is involved in many different cellular events, ranging from amino acid transport to cell-cell adhesion. Little is known about the positive and negative signalling pathways involved in these responses. Therefore, we examined the role of conventional protein kinase C (PKC) isoforms during CD98-induced intracellular signalling and homotypic aggregation of U937 cells. The CD98-induced aggregation was enhanced by the general protein kinase inhibitors GF109203X and staurosporin, and by specific PKC-alpha/-beta peptide inhibitor 19-27, but inhibited by PKC activators such as phorbol 12-myristate 13-acetate (PMA). PMA-inhibition was reversed by PKC inhibitors recognising the ATP-binding site in PKC (e.g. staurosporin, GF109203X and Go6983). Inhibitors which bind to diacylglycerol (DAG) or Ca(2+)-binding sites of PKC (calphostin C and Go6967) had no effect. PMA-induced translocation of conventional PKC (cPKC) isozymes (alpha, beta and gamma), but decreased the expression of PKC-delta, which plays an important role in CD98-induced homotypic aggregation. PMA treatment also suppressed the surface level of CD98 but not CD29, CD18 and CD147, dose- and time-dependently. These data provide evidence that PMA-responsive cPKC isoforms (alpha, beta and gamma) play a key role in negative regulation of CD98 signalling and homotypic aggregation.

Molecular association of CD98, CD29, and CD147 critically mediates monocytic U937 cell adhesion

“…The activation of these molecules by ligation with homotypic or heterotypic ligands is reported to induce intracellular signaling pathways leading to functional activation of monocytes playing a critical roles in inflammation and virus-derived fusion events [8]. Activation signals of monocytes induced by these adhesion molecules include small GTPase Rho, tyrosine kinases (Syk and Lyn), and the phosphatidylinositol-3-kinase during CD29 activation [910], ERK, Syk, and protein kinase Cθ in CD43 activation [1112], conventional PKC isoforms (α, β, γand δ), ERK, and p38 in case of CD98 stimulation [111314], and VEGFR-2 tyrosine kinase receptor, PI3K, AKT, and ERK1/2 under CD147 activation conditions [151617]. …”