P21-activated kinase 4 in pancreatic acinar cells is activated by numerous gastrointestinal hormones/neurotransmitters and growth factors by novel signaling, and its activation stimulates secretory/growth cascades

Abstract

p21-activated kinases (PAKs) are highly conserved serine/threonine protein kinases, which are divided into two groups: group-I (PAKs1-3) and group-II (PAKs4-6). In various tissues, Group-II PAKs play important roles in cytoskeletal dynamics and cell growth as well as neoplastic development/progression. However, little is known about Group-II PAK's role in a number of physiological events, including their ability to be activated by gastrointestinal (GI) hormones/neurotransmitters/growth factors (GFs). We used rat pancreatic acini to explore the ability of GI hormones/neurotransmitters/GFs to activate Group-II-PAKs and the signaling cascades involved. Only PAK4 was detected in pancreatic acini. PAK4 was activated by endothelin, secretagogues-stimulating phospholipase C (bombesin, CCK-8, and carbachol), by pancreatic GFs (insulin, insulin-like growth factor 1, hepatocyte growth factor, epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor), and by postreceptor stimulants (12-O-tetradecanoylphobol-13-acetate and A23187 ). CCK-8 activation of PAK4 required both high- and low-affinity CCK-receptor state activation. It was reduced by PKC-, Src-, p44/42-, or p38-inhibition but not with phosphatidylinositol 3-kinase-inhibitors and only minimally by thapsigargin. A protein kinase D (PKD)-inhibitor completely inhibited CCK-8-stimulated PKD-activation; however, stimulated PAK4 phosphorylation was only inhibited by 60%, demonstrating that it is both PKD-dependent and PKD-independent. PF-3758309 and LCH-7749944, inhibitors of PAK4, decreased CCK-8-stimulated PAK4 activation but not PAK2 activation. Each inhibited ERK1/2 activation and amylase release induced by CCK-8 or bombesin. These results show that PAK4 has an important role in modulating signal cascades activated by a number of GI hormones/neurotransmitters/GFs that have been shown to mediate both physiological/pathological responses in acinar cells. Therefore, in addition to the extensive studies on PAK4 in pancreatic cancer, PAK4 should also be considered an important signaling molecule for pancreatic acinar physiological responses and, in the future, should be investigated for a possible role in pancreatic acinar pathophysiological responses, such as in pancreatitis. NEW & NOTEWORTHY This study demonstrates that the only Group-II p21-activated kinase (PAK) in rat pancreatic acinar cells is PAK4, and thus differs from islets/pancreatic cancer. Both gastrointestinal hormones/neurotransmitters stimulating PLC and pancreatic growth factors activate PAK4. With cholecystokinin (CCK), activation is PKC-dependent/-independent, requires both CCK-R affinity states, Src, p42/44, and p38 activation. PAK4 activation is required for CCK-mediated p42/44 activation/amylase release. These results show PAK4 plays an important role in mediating CCK physiological signal cascades and suggest it may be a target in pancreatic acinar diseases besides cancer.

PAK6 promotes cervical cancer progression through activation of the Wnt/β‑catenin signaling pathway

“…PAKs have been discovered to serve important roles in numerous cellular biological processes, including cell cycle regulation, cell polarity, cytoskeletal reorganization, gene transcription and translation (21). More importantly, PAKs were reported to be overexpressed in numerous types of human malignancy, such as colon and breast cancers (22)(23)(24). The present study discovered that the expression levels of PAK6 were upregulated in cervical cancer tissues, and that the downregulation of PAK6 expression levels by shRNA decreased cell growth and proliferation, and inhibited the migratory and invasive abilities of HeLa cells.…”

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and β-catenin in rat pancreatic acinar cells

“…The Group I PAKs have been extensively studied and have been shown to have important roles in numerous diverse cellular processes in both normal cells (i.e., cell survival/apoptosis/ growth, motility, protein synthesis, glucose homeostasis, secretion) and in pathologic conditions, including tumor growth/ proliferation/invasiveness (44,98). The Group II kinases, although less well studied than the Group I PAKs in normal tissues, have also been reported to play diverse roles in numerous normal cellular functions, such as cell cycle control, control of membrane recycling, cell migration, and survival (16,61). In contrast, Group II PAKs have been particularly well studied in neoplastic processes, where they have been shown to be overexpressed in many common tumors (pancreas, prostate, stomach, and other GI tumors) and their activation to be important in oncogenic transformation, tumor invasion, progression, and resistance (42,44,51,52,74).…”

“…Recent studies demonstrate that both Group I (PAK2) and Group II PAKs (PAK4) are present in pancreatic acinar tissue, and both are activated by gastrointestinal hormones and neurotransmitters, as well as by various pancreatic growth factors (61,86). Furthermore, their activation is important in the mediation of both growth cascades and secretion stimulated by CCK, a physiological mediator of pancreatic acinar function (11,38,61,86,89).…”

The Role of p21-Activated Kinases in Cancer and Beyond: Where Are We Heading?

“…PAK2 and PAK4 were activated by gastrointestinal hormones/neurotransmitters and growth factors in pancreatic acinar diseases. And thus PAK2/PAK4 may be new therapeutic targets for the treatment of diseases involved in deregulation of pancreatic acinar cells ( Nuche-Berenguer et al, 2016 ; Ramos-Alvarez and Jensen, 2018 ). PAK signaling pathway was reported to be involved in WNT and G-protein signaling in type 2 diabetes mellitus (T2DM) ( Dammann et al, 2018 ).…”

“…This activation of PAK2 stimulates several signal cascades including MAPK, FAK, and PI3K–Akt pathways to mediate physiological or pathophysiological responses related to the onset of pancreatitis, which can be inhibited by a PAK inhibitor, suggesting that PAK2 can act as a new therapeutic target for the treatment of pancreatic acinar diseases ( Nuche-Berenguer et al, 2016 ). Except the PAK2-mediated signaling pathways in pancreatic acinar cells, PAK4 can also be activated by stimulation of CREB, the VIP-/secretin-preferring receptors via EPAC, as well as regulate β-catenin signaling pathway to participate in Na + and K + -ATPase activation, mediating the pancreatic fluid secretion ( Supplementary Figure 3D ; Ramos-Alvarez and Jensen, 2018 ; Ramos-Alvarez et al, 2019 , 2020 ). These results together illustrate that PAKs play important roles in pancreatitis and pancreatic cancer growth, as well as enzyme secretion.…”