The high mobility group protein HMG20A cooperates with the histone reader PHF14 to modulate TGFβ and Hippo pathways

Abstract

High mobility group (HMG) proteins are chromatin regulators with essential functions in development, cell differentiation and cell proliferation. The protein HMG20A is predicted by the AlphaFold2 software to contain three distinct structural elements, which we have functionally characterized: i) an amino-terminal, intrinsically disordered domain with transactivation activity; ii) an HMG box with higher binding affinity for double-stranded, four-way-junction DNA than for linear DNA; and iii) a long coiled-coil domain. Our proteomic study followed by a deletion analysis and structural modeling demonstrates that HMG20A forms a complex with the histone reader PHF14, via the establishment of a two-stranded alpha-helical coiled-coil structure. siRNA-mediated knockdown of either PHF14 or HMG20A in MDA-MB-231 cells causes similar defects in cell migration, invasion and homotypic cell–cell adhesion ability, but neither affects proliferation. Transcriptomic analyses demonstrate that PHF14 and HMG20A share a large subset of targets. We show that the PHF14-HMG20A complex modulates the Hippo pathway through a direct interaction with the TEAD1 transcription factor. PHF14 or HMG20A deficiency increases epithelial markers, including E-cadherin and the epithelial master regulator TP63 and impaired normal TGFβ-trigged epithelial-to-mesenchymal transition. Taken together, these data indicate that PHF14 and HMG20A cooperate in regulating several pathways involved in epithelial–mesenchymal plasticity.

The H2A.Z and NuRD associated protein HMG20A controls early head and heart developmental transcription programs

“…As expected, the N-terminal domain of HMG20A that contains the HMG box is indeed capable of binding free DNA (Fig. 2D ), in agreement with recent reports in which the full-length HMG20A protein was used 30 or in which the HMG box was demonstrated to bind with high affinity to double-stranded, four-way-junction DNA 31 .…”

“…TEAD1, which is one of the core cardiac transcription factors in heart development 39 was also repeatedly detected in our HMG20A interactome data sets and recently described to bind to HMG20A 31 . Apart from these interacting partners that we identified, HMG20A was also shown to bind to Ca2 + /S100A6, a protein that contributes to cellular calcium signalling 53 .…”

“…In line with our finding, a previous study reported that HMG20A is required for SNAI1-mediated EMT by replacing HMG20B, while its loss induces reversion of the EMT signaling program 28 . Also, another report which was published during the revision process of this manuscript showed that loss of HMG20A impairs TGFβ-triggered EMT 31 .…”

“…9 , middle). Thus, it is tempting to speculate about two working contexts (at least in HeLaK cells) for HMG20A, one in which HMG20A associates with PHF14 of the PRTH complex 31 and the M1HR complex at H2A.Z/PWWP2A 18 -cobound promoters, and a second at intronic enhancer sites where it interacts with the complete NuRD and the BHC/CoREST complexes and possibly also TEAD, L3MBTL3 and BEND3, as those are also not found in H2A.Z or PWWP2A interactomes. However, HMG20A appears to co-localize with MTA1, CHD4 and LSD1 at H2A.Z-positive regulatory regions in mESCs, suggesting that such a clear distinction cannot be made in all cell types.…”

“…Given the highly similar motifs found in both HMG20A-only and HMG20A + H2A.Z binding sites and the failure of the HMG box-containing N-terminus to pull-down chromatin, it is unlikely that DNA sequence alone is the primary factor determining HMG20A’s chromatin targeting. However, future studies will be needed to evaluate whether other interacting proteins, such as BHC/CoREST, NuRD subunits, PRTH members, PWWP2A, H2A.Z and others, help to target/attach HMG20A to distinct regulatory regions, maybe even in combination with specific DNA sequences and structure 31 .…”