STIMULATION OF RECEPTOR-ASSOCIATED KINASE, TYROSINE KINASE, AND MAP KINASE IS REQUIRED FOR PROLACTIN-MEDIATED MACROMOLECULAR BIOSYNTHESIS AND MITOGENESIS IN NB2 LYMPHOMA
Gb. Carey et Jp. Liberti, STIMULATION OF RECEPTOR-ASSOCIATED KINASE, TYROSINE KINASE, AND MAP KINASE IS REQUIRED FOR PROLACTIN-MEDIATED MACROMOLECULAR BIOSYNTHESIS AND MITOGENESIS IN NB2 LYMPHOMA, Archives of biochemistry and biophysics, 316(1), 1995, pp. 179-189
Lactogens [prolactin (Prl) and growth hormone] stimulate phosphorylati
on of the 40S ribosomal protein, S6, in Nb2 cells by mechanisms that d
o not involve participation of cAMP or protein kinase A, protein kinas
e C, or cGMP-dependent protein kinase. However, inhibition of tyrosine
kinase (TK) abrogates Prl-mediated macromolecular biosynthesis. Inasm
uch as lactogen signaling may involve sequential activation of protein
kinases, the effect of Prl on the well-characterized mitogen-activate
d protein kinase (MAPK) and S6 kinase (S6K), the enzyme responsible fo
r S6 phosphorylation in vivo, and their relationship to Nb2 macromolec
ular biosynthesis and mitogenesis were investigated. The results show
that MAPK stimulation is transient (peak activity, 30 min) and precede
s that of S6K, which reaches a maximum at 1.5-2 h, and slowly returns
towards control levels at 6 h. Both staurosporine which inhibits GH re
ceptor-associated kinase (JAK2) and genistein (GEN), an inhibitor of m
embrane-associated and cytoplasmic TRs, abrogate Prl-stimulated TK, MA
PK, and S6K. Rapamycin (RAP), a specific inhibitor of p70(S6K), comple
tely blocks S6K but does not affect TK and MAPK. TR and MAPK activity
correlates with Prl-stimulated anabolism, i.e., protein and DNA synthe
sis and mitogenesis. Thus, concentrations of STR and GEN which abrogat
e TK and MAPK inhibit anabolism virtually 100%. However, RAP, which in
hibits S6K (ca. 100%) but not TK or MAPK, only delays Prl-mediated ana
bolism. These results indicate that Prl signaling in Nb2 cells involve
s a protein kinase cascade and that regulation of receptor-associated
kinase, TK, and MAPK correlates with anabolism, The role of S6K (and S
6 phosphorylation) appears to be ancillary. (C) 1995 Academic Press, I
nc.