An RNA binding protein, RNP1A, works with Contractility Kit proteins to facilitate macropinocytosis

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, allowing for cell adaptation. In Dictyostelium discoideum, mechanoresponsive network proteins include Cortexillin I and IQGAP1, which assemble in the cytoplasm into macromolecular complexes, which we term Contractility Kits. In vivo fluorescence cross-correlation spectroscopy revealed that Cortexillin I also interacts with an RNA-binding protein, RNP1A. The rnp1A knockdown cells have reduced cell growth rate, reduced adhesion, defective cytokinesis, and a gene expression profile that indicates rnp1A knockdown cells shift away from the vegetative growth state. RNP1A binds to transcripts encoding proteins involved in macropinocytosis. One of these, DlpA, facilitates macropinosome maturation, similar to RNP1A. Loss of different CK proteins leads to macropinocytotic defects characterized by reduced macropinocytotic crown size. RNP1A interacts with IQGAP1 in vivo and has cross-talk with IQGAP1 during macropinocytosis. Overall, RNP1A contributes to macropinocytosis, in part through interacting with transcripts encoding macropinocytotic proteins like dlpA, and does so in coordination with the Contractility Kit proteins.