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The expression and activation of the Ste20-like kinase, SLK, is increased during renal development and recovery from ischemic acute renal failure. SLK promotes apoptosis, and during renal injury and repair, transcriptional induction or posttranscriptional control of SLK may, therefore, regulate cell survival. SLK contains protein interaction (coiled-coil) domains, suggesting that posttranslational homodimerization may also modulate SLK activity. We therefore expressed coiled-coil regions in the C-terminal domain of SLK as fusion proteins and demonstrated their homodimerization. By gel-filtration chromatography, endogenous and heterologously expressed SLK were detected in a macromolecular protein complex. To test the role of homodimerization in kinase activation, we constructed a fusion protein consisting of the SLK catalytic domain (amino acids 1-373) and a modified FK506 binding protein, Fv (Fv-SLK 1-373). Addition of AP20187 (an analog of FK506) enhanced the homodimerization of Fv-SLK 1-373. In an in vitro kinase assay, the dimeric Fv-SLK 1-373 displayed greater kinase activity than the monomeric form. In cells expressing Fv-SLK 1-373, homodimerization increased activation-specific phosphorylation of the proapoptotic kinases, c-Jun N-terminal kinase and p38 kinase. Compared with the monomer, dimeric Fv-SLK 1-373 enhanced the activation of a Bax promoter-luciferase reporter. Finally, expression of Fv-SLK 1-373 induced apoptosis, and the effect was increased by homodimerization. Thus the activity, downstream signaling, and functional effects of SLK are enhanced by dimerization of the kinase domain. [ABSTRACT FROM AUTHOR]

Abstract: Urotensin II (UII) and urotensin-related peptide (URP) are vasoactive neuropeptides with wide ranges of action in the normal mammalian lung, including the control of smooth muscle cell proliferation. UII and URP exert their actions by binding to the G-protein coupled receptor-14 known as UT. Lymphangioleiomyomatosis (LAM) is a disease of progressive lung destruction resulting from the excessive growth of abnormal smooth muscle-like cells that exhibit markers of neural crest origin. LAM cells also exhibit inactivation of the tumor suppressor tuberin (TSC2), excessive activity of ‘mammalian target of rapamycin (mTOR), and dysregulated cell growth and proliferation. In the present study we examined the expression and distribution of UII and UT in the lungs of patients with LAM. There was abundant expression of UII, URP and UT proteins in the interstitial nodular lesions of patients with LAM. By immunohistochemistry, UII, URP and UT were co-localized with HMB45, a diagnostic marker of LAM. Immunoreactivity for UII, URP and UT was also evident over the pulmonary epithelium, pulmonary vasculature and inflammatory cells. Western blotting revealed the presence of greater UT expression in the lungs of patients with LAM compared to normal human lungs. UT expression correlated with mTOR activity, as indicated by increased phosphorylation of S6 in LAM samples. These findings demonstrate for the first time the presence of UII, URP and their receptor in the lesions of patients with LAM, and suggest a possible role in the pathogenesis of the disease. [Copyright &y& Elsevier]

Discusses the clinical characteristics of lymphangioleiomyomatosis (LAM), the association of LAM and tuberculosis sclerosis complex (TSC), the morphologic characteristics of abnormal smooth muscle proliferative lesions, as well as gene and protein abnormalities that are characteristic of both sporadic LAM and LAM in patients with TSC.