The Action of Adenosine Analogs on PC12 Cells

Abstract

PC12 cells, a nerve growth factor-responsive clone of rat pheochromocytoma, contain a membrane-bound adenylate cyclase, which can be activated by adenosine analogs. The characteristics of the cyclase response indicate the presence of stimulatory adenosine receptors. Adenosine analogs also produce a marked increase in the ornithine decarboxylase levels of the cells, and the characteristics of this response suggest that it is linked to the adenylate cyclase-stimulatory adenosine receptors. The ornithine decarboxylase response elicited by 5'-N-ethylcarboxamideadenosine (NECA), a potent stimulatory adenosine analog, is synergistic with that produced by nerve growth factor. Differentiation of the cells with nerve growth factor, however, does not substantially alter either the response of cyclase to the adenosine analog or the magnitude of the adenosine-evoked ornithine decarboxylase response. Treatment of the cells with NECA produces an increase in the phosphorylation of a specific non-histone nuclear protein. While causing little or no morphological alteration by itself, NECA is synergistic with nerve growth factor in producing neurite outgrowth in PC12 cells. NECA does not cause an induction of acetylcholinesterase in the cells. NECA does not cause an induction of acetylcholinesterase in the cells, nor does it appear to affect the induction of this enzyme by nerve growth factor.

Clonal variants of PC12 pheochromocytoma cells with defects in cAMP-dependent protein kinases induce ornithine decarboxylase in response to nerve growth factor but not to adenosine agonists.

“…To determine whether the mutant cells were functionally defective in any of the responses thought to be regulated by cAMP, we measured the ability of wild-type PC12 cells and each of the mutants to induce ODC in response to increasing concentrations of phenylisopropyladenosine (PIA) or chloroadenosine. These agents are potent agonists for the adenosine-dependent adenylate cyclase (23). Data shown in Fig.…”

“…There have been reports that NGF (41,42), as well as adenosine and adenosine analogs (17,23), increase the activity of adenylate cyclase. Cyclic AMP (cAMP) and its derivatives have been shown to increase ODC levels (23), alter nuclear protein phosphorylations (14,24), elicit extension of neurites (4,27,28), and increase tyrosine hydroxylase activity (16).…”

“…Cyclic AMP (cAMP) and its derivatives have been shown to increase ODC levels (23), alter nuclear protein phosphorylations (14,24), elicit extension of neurites (4,27,28), and increase tyrosine hydroxylase activity (16). However, the issue of whether NGF alone increases cAMP levels is still not resolved.…”

A New Site and Mechanism of Action for the Widely Used Adenylate Cyclase Inhibitor SQ22,536

“…Therefore, these data suggest that SQ22,536 also inhibits an additional target situated downstream of AC. NGF induces neuritogenesis in neuroendocrine cells via a cAMP-independent mechanism (Guroff et al, 1981;Richter-Landsberg and Jastorff, 1986;Damon et al, 1990;Ginty et al, 1991). As seen in Fig.…”

Mutants of PC12 cells with altered cyclic AMP responses.

“…In response to nerve growth factor, the tumor cells undergo striking morphological and functional changes and develop into cells resembling neurons (34). The cells synthesize cAMP in response to the activation of an adenosine receptor coupled to adenylate cyclase (17), but the effect of nerve growth factor on cAMP content is inconsistent and of small magnitude (34). The cyclic nucleotide has been proposed to serve as a permissive or synergistic factor rather than to function as an obligatory intermediate (16), but other evidence supports dissociation of effects of cAMP and of nerve growth factor (14,20,30).…”