MAPK superfamily activation in human airway smooth muscle: mitogenesis requires prolonged p42/p44 activation

Abstract

Asthma is frequently associated with abnormal airway smooth muscle (ASM) growth that may contribute to airway narrowing and hyperresponsiveness to contractile agents. Although numerous hormones and cytokines have been shown to induce human ASM (HASM) proliferation, the cellular and molecular mechanisms underlying HASM hyperplasia are largely unknown. Here we characterize the roles of the mitogen-activated protein kinase (MAPK) superfamily [p42/p44 MAPK, c-Jun amino-terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38] in mediating hormone- and cytokine-induced HASM proliferation. Significant enhancement of [3H]thymidine incorporation in HASM cultures was observed only by treatment with agents (epidermal growth factor, platelet-derived growth factor, thrombin, and phorbol 12-myristate 13-acetate) that promoted a strong and sustained activation of p42/p44 MAPK. Significant activation of the JNK/SAPK and p38 pathways was only observed on stimulation with interleukin (IL)-1β and tumor necrosis factor-α, agents that did not appreciably stimulate HASM proliferation. Two different inhibitors of MAPK/extracellular signal-regulated kinase kinase (MEK), PD-98059 and U-0126, inhibited mitogen-induced [3H]thymidine incorporation in a manner consistent with their ability to inhibit p42/p44 activation. Elk-1 and activator protein-1 reporter activation by mitogens was similarly inhibited by inhibition of MEK, suggesting a linkage between p42/p44 activation, transcription factor activation, and HASM proliferation. These findings establish a fundamental role for p42/p44 activation in regulating HASM proliferation and provide insight into species-specific differences observed among studies in ASM mitogenesis.

Mechanisms of serum potentiation of GM-CSF production by human airway smooth muscle cells

“…ASMC proliferation in response to known mitogens such as PDGF and EGF is dependent on activation of the p42/p44 MAPK (17). Results from other studies indicate that the regulation of cytokine-mediated cytokine release also involves the MAPKs.…”

“…The studies with SB-203580 were conducted in duplicate and following 30-min incubation with SB-203580 or serum-free medium, cells were stimulated with 10% human serum for 15 min. Cells were lysed and analyzed by Western blotting using specific monoclonal antibodies against p38 and phospho-p38 (Thr 180 /Tyr 182 ) performed as previously described (17).…”

“…Agents found within human serum/plasma such as insulin-like growth factor (IGF) (14), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and thrombin have been shown to cause the proliferation of airway smooth muscle cells (ASMC) (17). Their effects on other airway smooth muscle functions, such as chemokine/cytokine production, are largely undetermined.…”

“…NF-B can be activated by the mitogen-activated protein kinases (MAPKs) p38 and p42/p44 (2), which also play a role in the release of cytokines (13). These MAPKs, particularly p42/p44, are also involved in the transduction of signals from mitogens found in serum/plasma resulting in cell proliferation (17). Recently, it has been demonstrated that the cytokine-induced release of GM-CSF by human ASMC can be reduced by inhibition of the MAPK JNK, clearly indicating a role for JNK in the regulation of cytokine-induced GM-CSF release (16).…”

PDGF-induced human airway smooth muscle cell proliferation requires STAT3 and the small GTPase Rac1

“…Previously, our laboratory determined that the signal transducers and activators of transcription (STAT) kinases, Jak and Src, are required for mitogen-induced signaling in human airway smooth muscle cells (HASMC) in vitro (43). Work done by others has demonstrated that the MAPK and PI3-kinase pathways, as well as Rac1, are also important in smooth muscle cell mitogenesis (31,32,35).…”