Epidermal growth factor‐induced phosphoinositide hydrolysis Modulation by protein kinase C

Abstract

A short-term treatment with phorbol 12,13-dibutyrate (PDBu) was found to inhibit totally the epidermal growth factor (EGF)-stimulated phosphoinositide hydrolysis in A431 cells, whereas long-term pretreatment with PDBu, which is known to down regulate protein kinase C, induced a greater accumulation of the EGF-triggered inositol phosphate accumulation, particularly of Ins(1,3,4,5)P,. The increased Ins(l,4,5)P3/Ins(l,3,4,5)P, formation in the PDBu long-term pretreated cells was coincident with the increased Caz+ Influx stimulated by EGF in the same cells. Since long-term pretreatment with PDBu was found to enhance the EGF signals, an explanation for the synergism between EGF and phorbol esters in the induction of DNA synthesis is provided.Epidermal growth factor; Inositol phosphate; Phorbol ester; (A431 cell)

Role of protein kinase C in the regulation of cytosolic Ca2+ in A431 cells: Separation of growth factor and bradykinin pathways

“…The effects observed on intracellular Ca 2+ release are consistent with the reported inhibition by TPA of PLC and IP 3 formation [1,2,6,9,27,33,34]. At lower concentrations of TPA (10 -~~ M), only the plasma membrane handling of Ca z+ was affected as evidenced by a reduced duration of the [Ca2+]~ plateau.…”

“…In quin-2 loaded A431 cells a short 5-10 rain treatment with TPA inhibits EGFinduced changes in [Ca2+];, suggesting that activation of PKC inhibits Ca 2+ entry [16]. Inositol phosphate production is also inhibited by 5-min treatment with TPA [33]. The same authors found treatment with phorbol ester for 24 hr resulted in an elevation of IP 3 and IP 4 production and elevation of [Ca2+]i [21].…”

“…We previously reported [37] that Ca 2+ entry and release from intracellular stores were readily observed using fura-2 methods but no EGFinduced IP 3 signal was observed. Other investigators have reported differences in A431 clones and shown a 50 to 100% increase in IP3 over the control [9,22,33]. Wahl and Carpenter [34] show that maximal production of IP 3 requires at least 75% receptor occupancy.…”

“…Here the initial rise in Ca 2 § was greater and there was no return of [Ca2+]i to baseline. The enhancement of the [Ca2+]~ transient might be due to the enhanced level of IP 3 or IP 4 following EGF stimulation in down regulated A431 cells [21,33]. Alternatively, PKC may play a role more directly in regulation of the intracellular Ca 2+ store response.…”

Effects of a sialoglycopeptide on early events associated with signal transduction

“…Reentry of quiescent cells into the cell cycle, and subsequent division, is thought to occur in response to growth factor binding to specific cell surface receptors that initiates a cascade of signal transduction events. These events include an activation of tyrosine-specific protein kinases (Hunter and Cooper, 1985;Zippel et al, 1986;Alexander and Cantrell, 19891, an activation of phospholipase C leading to an increased breakdown of phosphoinositides and the generation of inositol 1,4,5-trisphosphate and diacylglcerol (Hart et al, 1988;Vicentini et al, 1988;Berridge and Irvine 19891, and a concomitant elevation of cytosolic Cad+ from intracellular stores or by cellular uptake (Moolenaar et al, 1983;Rozengurt, 1986;Housley et al, 1988).…”