Pathogenic DVL frameshifting variants in Robinow syndrome disrupt WNT signaling and cellular dynamics

Abstract

Robinow syndrome (RS) is a genetically heterogeneous rare disorder involving six genes in the WNT/planar cell polarity (PCP) signaling pathway. Frameshifting variants in DVL genes that introduce a novel basic C-terminus are a common cause of autosomal dominant RS, accounting for [~]33% of individuals without ROR2 variants. Here, we review ClinVar and literature variants affecting DVL paralogs resulting in RS and investigate the cellular effects of pathogenic DVL frameshift variants with mutant tails replacing at least 82 amino acids. In silico analysis of the new C-termini revealed altered intrinsically disordered regions (IDRs), charge distribution, and predicted protein structures. To explore potential altered biological mechanisms caused by novel C-termini, we generated wild-type (WT), frameshift, and truncated constructs of DVL1-3, and analyzed their behavior in a transfection-based in vitro systems. DVL proteins normally polymerize into cytoplasmic puncta that redistribute upon WNT stimulation. Immunocytochemistry showed that mutant DVL proteins failed to change their localization in response to WNT ligands, in contrast to WT alleles--a consistent observation across all three DVLs. In line with this, TOPFlash reporter assays demonstrated that mutant DVL1 and DVL3 failed to activate canonical WNT signaling, while WT proteins induced strong activation. Additionally, the mutant C-terminal tail interfered with CSNK1E-induced phosphorylation, offering a potential mechanism underlying the impaired WNT response. Our results provide further understanding of the cellular consequences of pathogenic DVL frameshifting variants and offers insights into the effects of such alleles on WNT signaling, and the perturbations thereof, that may lead to developmental phenotypes observed in RS.