Stretch Activates Human Myometrium via ERK, Caldesmon and Focal Adhesion Signaling

Abstract

An incomplete understanding of the molecular mechanisms responsible for myometrial activation from the quiescent pregnant state to the active contractile state during labor has hindered the development of effective therapies for preterm labor. Myometrial stretch has been implicated clinically in the initiation of labor and the etiology of preterm labor, but the molecular mechanisms involved in the human have not been determined. We investigated the mechanisms by which gestation-dependent stretch contributes to myometrial activation, by using human uterine samples from gynecologic hysterectomies and Cesarean sections. Here we demonstrate that the Ca requirement for activation of the contractile filaments in human myometrium increases with caldesmon protein content during gestation and that an increase in caldesmon phosphorylation can reverse this inhibitory effect during labor. By using phosphotyrosine screening and mass spectrometry of stretched human myometrial samples, we identify 3 stretch-activated focal adhesion proteins, FAK, p130Cas, and alpha actinin. FAK-Y397, which signals integrin engagement, is constitutively phosphorylated in term human myometrium whereas FAK-Y925, which signals downstream ERK activation, is phosphorylated during stretch. We have recently identified smooth muscle Archvillin (SmAV) as an ERK regulator. A newly produced SmAV-specific antibody demonstrates gestation-specific increases in SmAV protein levels and stretch-specific increases in SmAV association with focal adhesion proteins. Thus, whereas increases in caldesmon levels suppress human myometrium contractility during pregnancy, stretch-dependent focal adhesion signaling, facilitated by the ERK activator SmAV, can contribute to myometrial activation. These results suggest that focal adhesion proteins may present new targets for drug discovery programs aimed at regulation of uterine contractility.

Smooth muscle 22α facilitates angiotensin II-induced signaling and vascular contraction

“…On the topic of ERK1/2 activity in cell contraction, previous researches have mainly focused on the upstream events that phosphorylate ERK1/2 [20]. It is reported that MKP3 regulated ERK1/2-mediated proliferation, development, and cell death through inactivation of ERK1/2 [15,21,22].…”

Distension of the uterus induces HspB1 expression in rat uterine smooth muscle

“…In the myometrium during pregnancy, uterine distension has been reported to increase the expression and/or posttranslational modification of CAPs, focal adhesion proteins, and signaling kinases, such as connexin43, FAK, and ERKs, respectively (25,26,(33)(34)(35). While investigation has been un- Fig.…”

“…The rat myometrium then undergoes the labor phase and becomes activated by the increased presence of contraction-associated proteins (CAPs), such as the gap junction protein connexin43 and oxytocin receptors, as well as decreased focal adhesion kinase (FAK) activity, thus marking the stabilization of myometrial cell-extracellular matrix (ECM) contacts to facilitate the initiation of labor (28,35,47). In this differentiation sequence, endocrine and mechanical pathways are required for induction of CAP gene expression (25,26,(33)(34)(35)43).…”

Estrogen Receptor β and Its Domains Interact with Casein Kinase 2, Phosphokinase C, and N-Myristoylation Sites of Mitochondrial and Nuclear Proteins in Mouse Brain

“…The 69 kDa protein has been identified as 18th day whole body protein (peaks-26, unique peptides-9, and mascot score-112), and acts as a homeodomain transcription factor in brain. The 61 kDa protein is a ankyrin protein (peaks-31, unique peptides-19 and mascot score-187), expressed in brain and plays a vital role in energy homeostasis (44). The 53 kDa protein is identified as bone marrow macrophage tRNA synthetase (peaks-35, unique peptides-22, and mascot score-192).…”