The RNA-binding protein RNP1A is essential and interacts with contractility kit proteins to facilitate cell mechanics.

Cell shape regulation is important for many biological processes. Some cell shape-regulating proteins harbor mechanoresponsive properties that enable them to sense and respond to mechanical cues. In Dictyostelium discoideum, mechanoresponsive network proteins formed by proteins such as myosin II, cortexillin I and IQGAP1 assemble in the cytoplasm into macromolecular complexes, which we term contractility kits (CKs). In our previous studies, we identified the RNA-binding protein RNP1A as a genetic interactor with the cytoskeletal machinery of the cell and as a biochemical interactor of cortexillin I, using in vivo fluorescence cross-correlation spectroscopy. In this study, we show that Dictyostelium rnp1A knockdown cells have reduced cell proliferation, reduced adhesion, defective cytokinesis, and a gene expression profile that indicates rnp1A knockdown cells shift away from the vegetative growth state. Some of the transcripts RNP1A binds encode proteins involved in macropinocytosis, a crucial cell shape change process. Loss of other CK proteins leads to macropinocytotic defects characterized by reduced macropinocytotic crown size. RNP1A interacts with IQGAP1, leading to crosstalk during macropinocytosis. Overall, RNP1A binds transcripts and contributes to cell mechanics and cell shape change processes through interactions with CK proteins.