Ribosomal Frameshifting Selectively Modulates the Biosynthesis, Assembly, and Function of a Misfolded CFTR Variant

Abstract

The cotranslational misfolding of the cystic fibrosis transmembrane conductance regulator chloride channel (CFTR) plays a central role in the molecular basis of cystic fibrosis (CF). The misfolding of the most common CF variant ({Delta}F508) remodels both the translational regulation and quality control of CFTR. Nevertheless, it is unclear how the misassembly of the nascent polypeptide may directly influence the activity of the translation machinery. In this work, we identify a structural motif within the CFTR transcript that stimulates efficient -1 ribosomal frameshifting and triggers the premature termination of translation. Though this motif does not appear to impact the interactome of wild-type CFTR, silent mutations that disrupt this RNA structure alter the association of nascent {Delta}F508 CFTR with numerous translation and quality control proteins. Moreover, disrupting this RNA structure enhances the functional gating of the {Delta}F508 CFTR channel at the plasma membrane and its pharmacological rescue by the CFTR modulators contained in the CF drug Trikafta. The effects of the RNA structure on {Delta}F508 CFTR appear to be attenuated in the absence of the ER membrane protein complex (EMC), which was previously found to modulate ribosome collisions during "preemptive quality control" of a misfolded CFTR homolog. Together, our results reveal that ribosomal frameshifting selectively modulates the assembly, function, and pharmacological rescue of a misfolded CFTR variant. These findings suggest interactions between the nascent chain, quality control machinery, and ribosome may dynamically modulate ribosomal frameshifting in order to tune the processivity of translation in response to cotranslational misfolding. SignificanceMany diseases stem from imbalances between protein synthesis and degradation that arise from mutations and/ or cellular stressors. The molecular mechanisms responsible for such lapses in cellular proteostasis often coincide with aberrant regulation of protein translation. Here, we identify a structure within the transcript encoding the CFTR chloride channel that allows the ribosome to halt translation in response to its cotranslational misfolding. We show that this motif modifies the assembly, function, and pharmacological properties of the most common cystic fibrosis variant. This crosstalk between the ribosome and nascent polypeptide allows the ribosome to adjust its activity to prevent the synthesis of misfolded proteins. These findings suggest ribosomal frameshifting and premature translational termination plays a fundamental role in protein quality control.