TGF-βs counteract hyaluronidase enhancement of TNF apoptosis but fail to restrict hyaluronidase blocking of staurosporine-mediated cell death

Murine L929 fibrosarcoma cells, when pretreated with hyaluronidase for at least 12 hr, acquired an increased cytostatic and apoptotic response to TNF-α. An enhanced growth inhibition was also observed in hyaluronidasepretreated cells when subsequently undergone serum deprivation. In contrast, hyaluronidase blocked staurosponne-mediated apoptosis when L929 cells were simultaneously exposed to both chemicals. However, hyaluronidase-pretreated cells could not resist staurosporine apoptosis (without the continuous presence of hyaluronidase). TGF-βs blocked hyaluronidase induction or TNF response. For instance, pretreatment of L929 cells with hyaluronidase in the presence of TGF-βl, -β2 or -β3 for 24 hr abolished the hyaluronidase-induced TNF sensitivity. Alternatively, hyaluronidase-pretreated cells lost their increased TNF sensitivity when exposed to TNF-α in the presence of TGF-βl, or briefly exposed to TGFβl followed by treating with TNF-α. Furthermore, TGF-β I-pretreated L929 cells failed to initiate an enhanced TNF response by hyaluronidase. TGF-βl is known to initiate protein-tyrosine phosphorylation and block TNF cytotoxic function (Chang, N.-S.,/ Biol. Chem., 270, 7765-7772, 1995). Inhibitors of protein-tyrosine kinases including lavendustin A and tyrphostin blocked TGF-βl counteracting the hyaluronidase-increased TNF sensitivity, whereas these inhibitors alone were ineffective in inhibiting hyaluronidase action. In contrast, TGF-βl failed to counteract hyaluronidase blocking of staurosporine apoptosis. Similarly, TGF-βl could not block hyaluronidase enhancement of serum starvation-mediated growth arrest. Despite the underlying mechanism is unknown, both TNF and staurosporine apparently initiate divergent pathways leading to cellular apoptosis. TGF-βl abolished hyaluronidase-increased TNF response in L929 cells by increasing cellular protein phosphorylation, thereby interrupting the eventual outcome of hyaluronidase action.