Date of Award
2025
Document Type
Honors Thesis (Open Access)
Department
Colby College. Biology Dept.
Advisor(s)
Christina Cota
Second Advisor
Lynn Hannum
Third Advisor
Andrea Tilden
Abstract
Cellular trafficking of receptors and associated membrane proteins is crucial for regulating cell signaling. As previous research has suggested that endocytic trafficking is shut down during cell division, few studies have investigated the regulation of membrane trafficking during mitosis, leaving the assumption of mitotic trafficking untested. In the model chordate, Ciona robusta, active cyclin-dependent kinase 1 (CDK1) inhibits the degradation of Fibroblast Growth Factor receptors (FGFRs), which are responsible for inducing cardiac cell fate during asymmetric pre-cardiac founder cell division. Our preliminary analysis in Ciona suggests that this CDK1-dependent inhibition may result from the phosphorylation of Rab7-GTPase, a protein necessary for delivering FGFRs to lysosomes for degradation. However, it is unclear whether this mechanism is unique to Ciona robusta. Here, I investigate whether cell cycle-dependent regulation of FGFR trafficking is conserved in mammalian systems. The results confirmed that the trafficking of human FGFR2 takes place during cell division and that active CDK1 inhibits FGFR2 degradation during this process in primary mouse keratinocytes. Motivated by our preliminary findings in Ciona, I used site-directed mutagenesis to mutate the putative CDK1 phosphorylation sites in the human Rab7a to generate phospho-deficient and phospho-mimetic Rab7a. To determine if CDK1 suppresses the degradation of FGFR during mitosis by phosphorylating Rab7a, I characterized the effects of mutant Rab7a proteins on mitotic FGFRs in cultured keratinocytes. Both phospho-deficient and phospho-mimetic Rab7a mutants impaired Rab7a function, altering its colocalization with FGFR2. These results support a model in which CDK1-mediated phosphorylation of Rab7a during mitosis inactivates Rab7a, leading to its dissociation from endosomal membranes and helping to promote FGFR2 storage by preventing the degradation of FGFR2. Our findings provide critical insight into the dynamics of mitotic FGFR2 trafficking in primary mouse keratinocytes and assess the role of Rab7a phosphorylation on mitotic FGFR2 degradation. Understanding how membrane trafficking dynamics are regulated during cell division is crucial to explore how dysregulation in trafficking through phosphorylation events might contribute to uncontrolled cell growth and cancer initiation.
Keywords
Cell signaling, Cell division, Receptor trafficking, FGFR, Rab7, CDK1-dependent Phosphorylation
Recommended Citation
Huynh, Tran H. and Cota, Christina D., "Cellular trafficking of Fibroblast Growth Factor receptors via CDK1-dependent phosphorylation of Rab7 during cell division in mouse keratinocytes" (2025). Honors Theses. Paper 1519.https://digitalcommons.colby.edu/honorstheses/1519