Interaction of PACAP with Sonic hedgehog reveals complex regulation of the Hedgehog pathway by PKA

Abstract

Sonic hedgehog (Shh) signaling is essential for proliferation of cerebellar granule cell progenitors (cGCPs) and its aberrant activation causes a cerebellar cancer medulloblastoma. Pituitary adenylate cyclase activating polypeptide (PACAP) inhibits Shh-driven proliferation of cGCPs and acts as tumor suppressor in murine medulloblastoma. We show that PACAP blocks canonical Shh signaling by a mechanism that involves activation of protein kinase A (PKA) and inhibition of the translocation of the Shh-dependent transcription factor Gli2 into the primary cilium. PKA is shown to play an essential role in inhibiting gene transcription in the absence of Shh, but global PKA activity levels are found to be a poor predictor of the degree of Shh pathway activation. We propose that the core Shh pathway regulates a small compartmentalized pool of PKA in the vicinity of primary cilia. GPCRs that affect global PKA activity levels, such as the PACAP receptor, cooperate with the canonical Shh signal to regulate Gli protein phosphorylation by PKA. This interaction serves to fine-tune the transcriptional and physiological function of the Shh pathway.

Structural and Morphometric Comparison of the Molar Teeth in Pre-eruptive Developmental Stage of PACAP-Deficient and Wild-Type Mice

“…In most experiments, PACAP behaves as an antagonist for bone morphogenetic protein-4 and SHH (Otto et al 2000;Nicot et al 2002;Lelievre et al 2006;Hirose et al 2011;Niewiadomski et al 2013), two of the main most widely studied signaling pathways of the tooth development (Dassule et al 2000;Jernvall and Thesleff 2000;Thesleff 2006;Bei 2009). Activation of PKA, regulated by PACAP receptors, can inhibit the transcriptional function of Gli1, consequently PACAP-induced signaling cascade is considered as a SHH signaling suppressor in neuronal elements (Hirose et al 2011;Niewiadomski et al 2013). In PACAP-deficient mice, the lower activation of the classical downstream signaling cascades of PAC1 receptor resulted in an elevated SHH signaling expression.…”

“…Moreover, it is proven in neuronal experimental models that downstream targets of PACAP receptors have a crosstalk with SHH signaling pathways. Binding of SHH to its receptor (PTCH1) can activate Gli1 transcription factor subsequently, induce several gene activation regulating proliferation and extracellular matrix production of cells (Tuson et al 2011;Christopher et al 2012;Niewiadomski et al 2013). The complexity of this regulation is still not fully understood since some neurotrophins are also involved in tooth development, for example, nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) (Mitsiadis and Luukko 1995;Luukko et al 1996Luukko et al , 1997Nosrat et al 1998Nosrat et al , 2002Iwamoto et al 2011).…”

The effect of cyclic phosphatidic acid on the proliferation and differentiation of mouse cerebellar granule precursor cells during cerebellar development

“…Shh plays an important role in the proliferation of GCPs as well as in the occurrence of medulloblastoma, the most common cerebellar tumor (Browd et al, 2006;Cordeiro et al, 2014;Dahmane and Ruiz i Altaba, 1999;Roussel and Hatten, 2011;Vaillant and Monard, 2009). Several extracellular factors, such as the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP), the cell adhesion molecule vitronectin, Wnt3, and the matricellular protein, NOV, are known to be suppressors of Shhdependent cell proliferation in the cerebellum (Anne et al, 2013;Le Dreau et al, 2009;Nicot et al, 2002;Niewiadomski et al, 2013;Pons et al, 2001;Vaillant and Monard, 2009). Although cPA is abundant in the central nervous system (Bandoh et al, 1999;Shan et al, 2008), the effect of cPA on GCPs in the cerebellum remains unknown.…”

Role of PACAP and VIP Signalling in Regulation of Chondrogenesis and Osteogenesis

“…In UMR-106 cells the application of PACAP elevated the expression of PTHrP without altering the IHH expression [ 14 ]. Sonic hedgehog (SHH) pathway is known to be regulated by PACAP signalling [ 60 ] and the activation of PKA downregulates the function of Gli1, which consequently decreases the proliferation [ 24 ] (Fig. 20.2 ).…”

“…The elevation of intracellular Ca 2+ concentration activates various Ca 2+ dependent signalling molecules such as classical PKCs, MAPK [ 19 ] or protein phosphatases like PP2B [ 20 ]. G-protein coupled receptors (GPCR) have been proven to have communication with other signalling cascades, implying that PACAP receptor activation may cross talk with WNT β-catenin [ 21 ], TGFβ [ 22 ], BMP [ 23 ], Hedgehog [ 24 ], and Notch signal transduction [ 25 ]. Multifactorial or pleiotropic effects of PACAP have been investigated in several biological processes and it has been proven to prevent apoptosis, ischemic conditions, infl ammation and oxidative stress [ 21 , 26 -29 ].…”