Integrin Linked Kinase (ILK) modulates SmMHC expression in tracheal smooth muscle tissues by regulating the activity of Serum Response Factor (SRF)

Abstract

Integrin-linked kinase (ILK) is a multi-domain protein kinase that binds to the cytoplasmic tail of beta integrins and signals to pathways that regulate cell growth and differentiation. We modulated ILK expression in tracheal muscle tissues and evaluated the effect on smooth muscle myosin heavy chain (SmMHC) expression. ILK antisense was used to depress ILK protein expression, and FLAG-ILK was expressed in smooth muscle tissues to increase ILK protein expression. ILK antisense treatment for 24 hrs caused the depletion of ILK protein by 30–40% and stimulated a two-fold increase in the expression of SmMHC protein. Real time RT-PCR of tissue extracts demonstrated a significant increase in SmMHC mRNA. Transfection with ILK-FLAG plasmids induced a 40–50% increase in ILK protein expression, inhibited SmMHC expression by 30–40% and decreased SmMHC mRNA. Immunofluorescence analysis and cell fractionation were used to evaluate the effect of modifications in ILK expression in the tissues on the cellular localization of the transcriptional regulator, SRF. More SRF fluorescence was observed in the nucleus of cells dissociated from ILK-depleted tissues relative to untreated tissues and more SRF was detected in nuclear extracts from ILK-depleted tissues. A ChIP assay confirmed increased binding of SRF to the SmMHC promoter in extracts from ILK-depleted tissues relative to undepleted tissues. Our results suggest that ILK is a negative modulator of SmMHC expression in airway smooth muscle, and that ILK decreases the amount of SRF that localizes to the nucleus and reduces SRF binding to the SmMHC promoter. Supported by HL 29289, HL074099, and AHA