The BBSome regulates cell proliferation by controlling cell cycle progression

Cell cycle progression can be divided into four phases: gap (G1), DNA synthesis (S), gap 2 (G2) and mitosis (M). Stimulation of cells with growth-promoting factors results in upregulation of the D-type cyclins, which activates the cyclin-dependent kinases (CDK) 4 and 6. Cyclin-D-CDK4/6 complexes, together with E-type cyclin and their associated kinases, are required for the entry and progression of cells into S phase. Bardet-Biedl syndrome (BBS) is a syndromic human disorder associated with several clinical features such as obesity and hypertension. Mice lacking Bb s genes recapitulated many BBS phenotypes including obesity. Previous work from our group demonstrated that BBSome (complex of 8 BBS proteins) deficiency delays wound healing and cell migration via a Cullin-3/RhoA pathway, and BBSome modulates the activity of dynamin-like protein 1 (DRP1), a key regulator of mitochondrial fission. However, it is not clear whether BBSome deficiency affects cell cycle and proliferation. To address this, we bioengineered BBSome deficient mouse hypothalamic N39 cells using CRISPR-cas9 to knock-out a component of the BBSome, BBS1. Additionally, we established human fibroblasts cell lines from skin samples derived from BBS patients carrying the M390R mutation in the BBS1 gene and control humans without the disease. Here, we show that growth rate of N39-BBS1KO cells was significantly slower (by 51.7% at day 4 and 58.4% at day 6) than N39 cells. Similarly, BBS1 M390R/M390R fibroblasts cells grew slower (by 35.8% at day 7) compared to control human fibroblasts cells. Western blot analysis revealed that both cyclin D3 and E protein expression were significantly lower in N39-BBS1KO cells compared to control cells. Cyclin E expression was significantly lower in BBS1 M390R/M390R fibroblasts cells compared to normal human fibroblasts cells. Importantly, this decrease in cyclin D and E protein expression in N39-BBS1KO cells was reversed by overexpression of an active form of DRP1 (DRP1S 637A ). Consistent with the slow rates of proliferation, analysis of the cell cycle using flow cytometry showed that for cells in serum free conditions overnight, 61% of the N39-BBS1KO cells were in G1 and 35% in S phase compared to 46% of the control N39 cells that were in G1 phase and 46% in S phase. In 10% FBS condition, 37% of N39 cells were in G1 phase, and 52% in S phase whereas 46% of N39BBS1KO cells in G1 phase and 44% in S phase, indicating that loss of Bbs1 gene causes a delay in the transition from G1 to S phase during cell cycle progression. Taken together, we conclude that BBSome is required for cell cycle regulation and that slow cell proliferation may contribute to delayed cell migration and wound healing processes in BBS. NIH, VA This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.