Synergistic actions of epidermal growth factor‐urogastrone and vasopressin in cultured aortic A‐10 smooth muscle cells

Abstract

In cultured rat aorta-derived A-10 cells, epidermal growth factor-urogastrone (EGF-URO) acts synergistically with arginine vasopressin (AVP) to augment the AVP-mediated release of 3H-arachidonate (3H-AA) from 3H-AA prelabeled cells. On its own, EGF-URO had no effect on AA release and had no effect on calcium influx or efflux either in the absence or presence of AVP. The synergistic action of EGF-URO was not affected by actinomycin D, cycloheximide, indomethacin, by the diacylglycerol lipase inhibitor U-57,908, or by the tyrosine kinase inhibitors genistein (GS) and tyrphostin (TP). TP did, nonetheless, completely abrogate 3H-thymidine incorporation triggered in the presence of EGF-URO. Although EGF-URO stimulated an increase in calpactin-II (lipocortin-I) phosphorylation in permeabilized cells, no such increase was detected in intact cells exposed to EGF-URO either alone or in combination with AVP, under conditions where EGF-URO augmented the action of AVP. The phospholipase A2 inhibitor, mepacrine, had no effect on AVP-mediated AA release, but abolished the synergistic action of EGF-URO. We conclude that in contrast with our previous results with gastric smooth muscle strips, wherein EGF-URO acts via the diacylglycerol lipase-mediated metabolism of diacylglycerol, and in keeping with observations with cultured mesangial cells, EGF-URO acts synergistically with AVP in A-10 cells via the activation of phospholipase A2. This synergistic action of EGF-URO does not appear to be due to increased levels of cyclooxygenase and would appear not to require increased tyrosine kinase activity.

Inhibition of transforming growth factor alpha stimulation of human squamous cell carcinoma of the head and neck with anti-TGF-α antibodies and tyrphostin

“…Based on the molecular weights of the phosphorylated proteins, the 180-kd glycoprotein is probably the EGF receptor, which is known to be autophosphorylated following binding of EGF (44). The 35-kd protein is equivalent in size to calpactin I (lipocortin II) (45) and calpactin II (lipocortin I) (44), two proteins that have been proposed to be involved in the signal transduction pathway for the EGF receptor (45,46 Initially confluent cultures of SCC cells were washed three times with PBS, solubilized in 1.5 ml of 1% Triton X-100 in PBS, centrifuged, and the supernatant retained. Serum-free conditioned medium (CM) was collected from initially confluent cultures of A-253, FaDu, and RPMI-2650 ceils.…”