Protocadherin-7 Regulates Osteoclast Differentiation through Intracellular SET-Binding Domain-Mediated RhoA and Rac1 Activation

Abstract

Protocadherin-7 (Pcdh7) is a member of the non-clustered protocadherin δ1 subgroup of the cadherin superfamily. Although the cell-intrinsic role of Pcdh7 in osteoclast differentiation has been demonstrated, the molecular mechanisms of Pcdh7 regulating osteoclast differentiation remain to be determined. Here, we demonstrate that Pcdh7 contributes to osteoclast differentiation by regulating small GTPases, RhoA and Rac1, through its SET oncoprotein binding domain. Pcdh7 is associated with SET along with RhoA and Rac1 during osteoclast differentiation. Pcdh7-deficient (Pcdh7−/−) cells showed abolished RANKL-induced RhoA and Rac1 activation, and impaired osteoclast differentiation. Impaired osteoclast differentiation in Pcdh7−/− cells was restored by retroviral transduction of full-length Pcdh7 but not by a Pcdh7 mutant that lacks SET binding domain. The direct crosslink of the Pcdh7 intracellular region induced the activation of RhoA and Rac1, which was not observed when Pcdh7 lacks the SET binding domain. Additionally, retroviral transduction of the constitutively active form of RhoA and Rac1 completely restored the impaired osteoclast differentiation in Pcdh7−/− cells. Collectively, these results demonstrate that Pcdh7 controls osteoclast differentiation by regulating RhoA and Rac1 activation through the SET binding domain.

PCDH7 Promotes Cell Migration by Regulating Myosin Activity

“…We also cannot exclude the possibility that PCDH7 suppresses myosin phosphatase activity by influencing Rho-ROCK modulators. A recent study reported that PCDH7 involves in the activation of Rho signaling during osteoclast differentiation (Kim et al, 2021). Further study is necessary to elucidate the molecular details of PCDH7 dependent regulation of myosin phosphatase activity.…”

ZDHHC5 targets Protocadherin 7 to the cell surface by a palmitoylation-dependent mechanism to promote successful cytokinesis

“…Recently, it has been reported that PCDH7 functions in osteoclast differentiation by regulating RhoA and Rac1. Loss of PCDH7 expression impairs RhoA activation in pre-osteoclasts (Kim et al, 2021). In agreement with those studies, we also observed that depletion of PCDH7 impairs active RhoA and myosin levels at the cleavage furrow.…”

PP2A-Mediated GSK3β Dephosphorylation Is Required for Protocadherin-7-Dependent Regulation of Small GTPase RhoA in Osteoclasts

“…Pcdh7 plays a crucial role in the activation of Rho-family small GTPases, RhoA and Rac1 in osteoclasts. Its intracellular domain, which is known for binding to the oncogene SET (SET/Template-activating factor 1 (TAF1)), is essential for regulating RhoA and Rac1 [20,21]. These findings provide evidence that Pcdh7 plays a role in osteoclast differentiation as a mediator of cell signaling.…”

“…The activity of PP2A and Rho-family small GTPase is reportedly linked through Glycogen synthase kinase-3β (GSK3β) in cancer cells [26][27][28]. Since Pcdh7 associates with RhoA and Rac1 through its intracellular SET binding domain and since the domain is critical for Pcdh7-mediated activation of RhoA and Rac1 during osteoclast differentiation [20], these observations suggest that PP2A plays a relevant role in Pcdh7-mediated signaling in osteoclasts.…”