HAN11 binds mDia1 and controls GLI1 transcriptional activity

The Hedgehog pathway is important in normal and diseased skin. One of the key transcription factors in the pathway is GLI1. GLI1-dependent transcription is positively regulated by DYRK1A, which is reported to bind HAN11. HAN11 is the human homologue of AN11, which controls flavonoid synthesis in plants.

We wanted to identify other binding partners of HAN11 and investigate whether HAN11 regulates GLI1-dependent transcription.

We used TAP-tag purification and GST pull down to identify protein-protein interactions and performed luciferase assays of transcriptional activity. We used immunofluorescence microscopy to examine the subcellular distribution of HAN11, mDia1 and GLI1. We performed in situ hybridisation to compare expression of HAN11 with GLI1 and patched in mouse embryos.

We identified the cytoskeletal regulator mDia1 as a binding partner of HAN11. We showed that HAN11 binds the FH2 actin binding domain of mDia1 and confirmed that HAN11 also interacts with DYRK1A. Overexpression of mDia1 or active RhoA caused translocation of HAN11 from nucleus to cytoplasm. HAN11 and mDia1 repressed DYRK1A-dependent GLI1 transcriptional activity. HAN11 overexpression decreased SZ95 sebocyte proliferation and increased cytoplasmic GLI1. AN11 was highly expressed in E10.5 mouse embryo limb buds, in an overlapping pattern with Ptc and GLI1.

These results suggest that AN11 may be a physiological regulator of GLI1 transcriptional activity.