Phosphorylation of prolactin and growth hormone

Abstract

To determine whether GH and prolactin could be phosphorylated, turkey GH, chicken GH, chicken prolactin and turkey prolactin were incubated in vitro with the catalytic subunit of protein kinase A and [gamma-32P]ATP. Phosphorylation was assessed after sodium dodecyl sulphate-polyacrylamide gel electrophoresis, Western blotting and autoradiography. Polyacrylamide electrophoresis showed that both purified native chicken GH and turkey GH were phosphorylated under the conditions employed. However, the glycosylated variant of chicken GH did not appear to be labelled. Chicken prolactin, turkey prolactin and the glycosylated variant of turkey prolactin were all intensely phosphorylated by protein kinase A. Ovine and rat prolactins could also be phosphorylated by protein kinase A. The phosphate content of different native prolactin (turkey, ovine and rat) and GH (ovine and chicken) preparations was also determined and found to be significant. Chicken pituitary cells in primary culture incorporated 32P in GH- and prolactin-like bands isolated by non-denaturing polyacrylamide gel electrophoresis, and this was stimulated by phorbol myristate acetate. Phosphorylation of GH and prolactin may thus explain some of the charge heterogeneity of these hormones.

The Effect of Estrogen on Phosphorylation of Prolactin in the Mouse Pituitary Gland

“…Other researchers have shown that the ratios of PPRL to PRL are constant within various species, such as 0.7:1.0 in turkeys and 0.2:1.0 in sheep and rats [5]. We compared the staining intensity of PPRL and non-phosphorylated PRL spots.…”

“…Anterior pituitary PRL undergoes phosphorylation in rats, humans [4], chickens, turkeys [5] and cattle [6]. Phosphate analysis of phosphorylated PRL ( P P R L ) h a s s h o w n t h a t t h e r a t i o o f n o nphosphorylated PRL to PPRL is species-specific [5,6].…”

“…Phosphate analysis of phosphorylated PRL ( P P R L ) h a s s h o w n t h a t t h e r a t i o o f n o nphosphorylated PRL to PPRL is species-specific [5,6]. Analysis of phosphorylation sites has demonstrated one at serine 179 th (177 th in rat) in human PRL [7].…”

S179D-Human PRL, a Pseudophosphorylated Human PRL Analog, Is an Agonist and Not an Antagonist

“…The occurrence in vivo of PRL phosphorylation has been clearly demonstrated in bovine pituitary (13), where serine 90 was identified as the major phosphorylation site of bovine PRL (14). In other species the in vivo demonstration of PRL phosphorylation has been less definitive (15,16), and the physiological relevance of phosphorylation sites identified by in vitro incorporation of 32 P into PRL (17,18) remains questionable. In humans, although pituitary-purified human PRL (hPRL) preparations obtained from the NIDDK were shown to contain traces of phosphorylated forms (19,20), definite identification of phosphorylated amino acid(s) awaits further investigation.…”

S179D prolactin diminishes the effects of UV light on epidermal gamma delta T cells

“…In rodents, greater than 95% of PRL exists as either an unmodified or a phosphorylated form (Ho et al, 1993 a,b). The presence of phosphorylated PRL in pituitary extracts or purified pituitary PRL has been directly demonstrated in human , ovine, bovine, rat, mouse and turkey pituitary extracts (Oetting et al, 1986;Brooks et al, 1990;Aramburo et al 1992). The proportion of total PRL that is phosphorylated is physiologically regulated (Ho et al, 1993 a,b), with states of high estrogen resulting in both increased PRL and reduced phosphorylation.…”