Interaction of Growth Hormone-activated STATs with SH2-containing Phosphotyrosine Phosphatase SHP-1 and Nuclear JAK2 Tyrosine Kinase

Abstract

Growth hormone (GH) rapidly stimulates tyrosine phosphorylation followed by serine/threonine phosphorylation of multiple cytoplasmic STAT transcription factors, including one, STAT5b, that is uniquely responsive to the temporal pattern of plasma GH stimulation in rat liver and is proposed to play a central role in the activation of male-expressed liver genes by GH pulses in vivo (Waxman, D. J., Ram, P. A., Park, S. H., and Choi, H. K. (1995) J. Biol. Chem. 270, 13262-13270). We now show that JAK2, the GH receptor-associated tyrosine kinase, is present both in the cytosol and in the nucleus in cultured liver cells and in rat liver in vivo and that GH-activated STAT3 but not STAT5b becomes associated with nuclear JAK2. GH is also shown to activate by 3-4-fold SHP-1, a phosphotyrosine phosphatase that contains two src homology 2 (SH2) domains. GH also induces nuclear translocation and binding of SHP-1 to tyrosine-phosphorylated STAT5b, suggesting that this GH-activated phosphatase may play a role in dephosphorylation leading to deactivation of nuclear STAT5b following the termination of a plasma GH pulse in male rat liver in vivo. No such association of SHP-1 with GHactivated STAT3 was detected, a finding that could help explain the marked desensitization of STAT3, but not STAT5b, to subsequent GH pulses following an initial GH activation event.

Regulation of Neutrophil Adhesion by Pituitary Growth Hormone Accompanies Tyrosine Phosphorylation of Jak2, p125FAK, and Paxillin

“…It is well established that GH is a physiological mediator of immune cell functions (15)(16)(17)(18)(19), and many of the actions of this stimuli are likely to be transduced through the Jak2 pathway (20,21,23). Although it has been reported that GH increases neutrophil adhesion, the possible mechanisms have not been examined (16).…”

“…Lacking intrinsic tyrosine kinase activity, the GHR recruits and activates a member of the Janus family of cytosolic kinases (JAKs) upon dimerization (20,21). In addition to the GHR and itself, Jak2 phosphorylates STATs (22,23). We and others have previously demonstrated that recombinant GH (rGH) primes and enhances respiratory burst function in human neutrophils through intracellular calcium increase (12, 24 -30).…”

The LIM/Homeodomain Protein Islet1 Recruits Janus Tyrosine Kinases and Signal Transducer and Activator of Transcription 3 and Stimulates Their Activities

“…However, Jaks are cytoplasmic proteins that associated with the cytokine receptors on the membranes, although a constitutive nuclear localization of Jaks also was previously reported (Lobie et al, 1996;Ram and Waxman, 1997;Ragimbeau et al, 2001). Recently, it was reported to be predominantly localized at the membrane (Behrmann et al, 2004).…”

“…On the other hand, Jak family members (Tyk2, Jak1, and Jak2) are generally regarded as membrane-bound or predominantly cytoplasmic proteins. However, subsequently, they also were reported to be constitutively localized in the nucleus (Lobie et al, 1996;Ram and Waxman, 1997;Ragimbeau et al, 2001). Recently, Behrmann et al (2004) examined the cellular localization of Jak1 in various cell types and concluded that the Jak1, as well as Jak2 and Tyk2, are predominantly localized at the membranes, with no significant amounts in the nucleus or in the cytoplasm.…”

Kinase activity and subcellular distribution of a chimeric green fluorescent protein-tagged Janus kinase 2

“…Some investigators have provided evidence that yellow fluorescent protein-chimeras containing JAK1, JAK2 or TYK2 are predominantly located at the cellular membrane [16,17]. On the other hand, other groups, whose investigations did not employ fluorescent chimeras, reported a nucleocytoplasmic distribution for JAK2 [18][19][20], while yet other investigators reported that hemagglutinin-tagged JAK2 was distributed in the cytoplasm but excluded from the nucleus [21]. In order to further examine these and other issues surrounding the properties of JAK2's catalytic properties in a cellular context, we sought to develop other approaches to produce the recombinant enzyme in various mammalian cells.…”