Compared to other CMGC kinases the dual-specificity, tyrosine phosphorylation-regulated kinases (DYRKs) represent an understudied family of protein kinases. Whilst DYRK1A has garnered more attention due to its links to Downs’ Syndrome and Alzheimer’s Disease, the other class I DYRK, DYRK1B, remains comparatively unexplored. Prior work in our lab has explored potential new DYRK1B substrates by utilising a phospho-SILAC screen. From this screen we identified two proteins of the same family, FAM117A and FAM117B, which along with the third family member (FAM117C/GLCCI1) have previously been identified as binding partners of class I DYRKs. FAM117 proteins have no clearly established biological function and so understanding interactions between DYRK1B and FAM117 proteins may help to elucidate further functions of DYRK1B and also identify roles of FAM117 proteins.

Here I establish that FAM117 proteins represent DYRK1B inducible phosphoproteins that rely on kinase activity of DYRK1B for their phosphorylation and shown that FAM117B represents a direct substrate of DYRK1B. Furthermore, I demonstrate that both class I and class II DYRKs are capable of inducing post-translational modifications, that likely represent phosphorylation, of FAM117 proteins. This is not a characteristic shared by all CMGC kinases, with only the closely related CLK3 driving similar FAM117 phosphorylation.

Whilst no 3D structures exist for FAM117 proteins, prediction software suggests they are highly disordered with many predicted phosphorylation sites. This high level of disorder suggests that stable expression of FAM117 proteins may rely on binding partners and/or modifications such as phosphorylation. Indeed, I show that phosphorylation of FAM117 proteins by DYRKs is associated with their increased expression in both short & long term overexpression systems as well as the endogenous proteins. Using FAM117B as a model FAM117 protein, I identify a high number of DYRK1B inducible phosphorylation sites, many of which are located in the PFAM domain which is conserved between FAM117 proteins. Additionally, the scaffold protein DCAF7, which mediates the interactions of class I DYRKs with their substrates, also binds FAM117 proteins and I demonstrate that FAM117 proteins, DYRK1B & DCAF7 form ternary complexes in cells.

Understanding FAM117 function and how their interaction with DYRK1B affects the functions of both proteins may help us to better understand their functions. I demonstrate that expression of FAM117 proteins disrupt the normal distribution of DYRK1B, each in different ways, and that all are capable of perturbing a normal DYRK1B function, in this case the promotion of processing body formation. From observing FAM117 localisation I also show that they partially co-localise with cytoskeletal proteins, such as tubulin, and show strong co-localisation with focal adhesion proteins. FAM117 proteins are reported to be capable of binding the microtubule protein DYNLL1 and work from our lab has identified the intermediate filament protein KANK2 as a possible DYRK1B interactor. Both of these have been suggested to link microtubules to focal adhesions. Here I demonstrate that both DYNLL1 and KANK2 immunoprecipitate with FAM117 proteins and DYRK1B, suggesting a role for DYRK1B and FAM117 proteins in the regulation of focal adhesions which in turn may affect cell adhesion and migration. Given the role of microtubules in regulating membrane organelle dynamics this binding to DYNLL1 may also provide an explanation for the dysregulation of processing bodies caused by FAM117 proteins.

These new insights into DYRKs, specifically DYRK1B, and FAM117 proteins are discussed further and used to suggest hypotheses for future investigation. Furthermore, the FAM117 proteins may serve as useful biomarkers for DYRK activation or inhibition.