Attenuation of relaxing response induced by pituitary adenylate cyclase-activating polypeptide in bronchial smooth muscle of experimental asthma.

Bronchomotor tone is regulated by contraction and relaxation of airway smooth muscle (ASM). A weakened ASM relaxation might be a cause of airway hyperresponsiveness (AHR), a characteristic feature of bronchial asthma. Pituitary adenylyl cyclase-activating polypeptide (PACAP) is known as a mediator that causes ASM relaxation. To date, whether or not the PACAP responsiveness is changed in asthmatic ASM is unknown. The current study examined the hypothesis that relaxation induced by PACAP is reduced in bronchial smooth muscle (BSM) of allergic asthma. The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated. Tension study showed a BSM hyperresponsiveness to acetylcholine in the OA-challenged mice. Both quantitative RT-PCR and immunoblot analyses revealed a significant decrease in PAC1 receptor expression in BSMs of the diseased mice. Accordingly, in the antigen-challenged group, the PACAP-induced PAC1 receptor-mediated BSM relaxation was significantly attenuated, whereas the relaxation induced by vasoactive intestinal polypeptide was not changed. These findings suggest that the relaxation induced by PACAP is impaired in BSMs of experimental asthma due to a downregulation of its binding partner PAC1 receptor. Impaired BSM responsiveness to PACAP might contribute to the AHR in asthma.

PIAS3 enhances the transcriptional activity of HIF-1α by increasing its protein stability.

The transcription factor hypoxia-inducible factor-1 (HIF-1) functions as a master regulator of hypoxic response by inducing the transcription of various genes responsible for cellular adaptation to hypoxia. In this study, we investigated the effects of protein inhibitor of activated STAT3 (PIAS3), a small ubiquitin-related modifier (SUMO) E3 ligase, on HIF-1-mediated transcriptional activation. We found that PIAS3 physically associated with HIF-1α. Moreover, PIAS3 overexpression enhanced the transcriptional activity of HIF-1α independently of its SUMO E3 ligase activity. Conversely, quantitative RT-PCR analysis showed that RNAi-mediated PIAS3 knockdown reduced the expression of HIF-1 target genes under hypoxia. In addition, PIAS3 knockdown induced the destabilization of HIF-1α protein, and the destabilization was reversed by the proteasome inhibitor MG132. Taken together, these results suggest that PIAS3 functions as a positive regulator of HIF-1α-mediated transcription by increasing its protein stability.