Phosphatidylinositol kinase regulation of airway smooth muscle cell proliferation

Up-regulation of cyclin D1 expression in asthma serum-sensitized human airway smooth muscle promotes proliferation via protein kinase C alpha

Abnormal hypertrophy and hyperplasia of airway smooth muscle cells play an important role in airway remodeling in chronic asthma. The authors' previous studies have indicated that protein kinase C alpha (PKC alpha) is involved in the proliferation of passively sensitized human airway smooth muscle cells (HASMCs). However, the underlying mechanisms remain unknown. Here, the authors examined the possible role of the alpha isoform of PKC in the control of cyclin D1 expression, using HASMCs passively sensitized on human atopic asthmatic serum as a model system. Cultured HASMCs were passively sensitized with serum from atopic asthmatic patients. Cell proliferation was measured by [(3)H]thymidine incorporation and an MTT assay. Cell cycle status was analyzed by flow cytometry. The mRNA and protein expression profiles of cyclin D1 were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting, respectively. Furthermore, the authors assessed the role of cyclin D1 in PKC alpha-induced HASMC proliferation by transfection with a recombinant cyclin D1 antisense construct. The activation of PKC alpha with phorbol myristate acetate (PMA), a PKC activator, up-regulated cyclin D1 expression and increased the proliferation of passively sensitized HASMCs. This effect was significantly decreased by specific inhibition of PKC alpha with Go6976. In addition, the authors showed that transfection with antisense cyclin D1 abolished PMA-induced G1/S progression and HASMC proliferation. These results demonstrate that PKC alpha promotes the proliferation of HASMCs sensitized with atopic asthmatic serum via up-regulation of cyclin D1 expression.

Targeting the phosphatidylinositol 3-kinase pathway in airway smooth muscle: rationale and promise

The phosphatidylinositol 3-kinase (PI3K) signaling pathway plays a critical role in regulating cell growth, proliferation, survival, and motility. Structural alterations, e.g. airway remodeling, in asthma and chronic obstructive pulmonary disease (COPD) are associated with increased airway smooth muscle (ASM) cell growth and proliferation due to the frequent stimulation of ASM by inflammatory mediators, contractile agonists, and growth factors. The critical role of the PI3K signaling pathway in regulating ASM cell growth and proliferation is well established. However, recent discovery of the tumor suppressor proteins tuberous sclerosis complex 1 (TSC1) and TSC2, also known as hamartin and tuberin, as downstream effectors of PI3K and upstream regulators of the mammalian target of rapamycin (mTOR) and S6 kinase 1(S6K1) shed a new light on the PI3K signaling cascade in regulating cell growth and proliferation. The activity of TSC1/TSC2 is regulated by growth factors, nutrients, and energy; thus, TSC1/TSC2 serves as a signaling module for protein translational regulation, cell cycle progression, and cell size, which are key events controlling cell growth and proliferation. This article highlights the potential contribution of the PI3K-TSC1/TSC2-mTOR/S6K1 pathway in smooth muscle remodeling. Pharmacologic manipulation of this signaling pathway could have a major impact on treatment of asthma and COPD.