Polo-like kinase 4 (PLK4) inhibition reverses the loss of primary cilia in human melanoma cells

Summary: Abstract Body: Polo-like kinase 4 (PLK4) is the master regulator of centriole biogenesis and its overexpression is associated with centriole overduplication and amplification in melanoma. Centrosomes are responsible for the formation of primary cilia, which are key sensory and signaling hair-like organelles found on the surface of most mammalian cells. Interestingly, primary cilia are frequently lost during melanoma development and progression, which has been shown to enhance pro-tumorigenic WNT/β-catenin signaling. Given the role of PLK4 in centrosome biology, we hypothesized that PLK4 overexpression is involved in loss of cilia in melanocytic cells and its inhibition will reinforce cilia and impart anti-melanoma response. We found that small molecule inhibition of PLK4 (CFI-400945 or centrinone B) or its CRISPR/CAS9 knockout significantly increased the number and length of cilia in A375 and G361 melanoma cells. This was associated with an anti-proliferative response of PLK4 inhibition in-vitro and in-vivo. Further, to identify the mechanisms associated with the observed effects, we employed a human primary cilia specific RT2 Profiler PCR Array (Qiagen) that contains 84 genes related to ciliary function signaling pathways, on CFI-400945-treated A375 and G361 cells. We found that CDKN1A (p21), IHH, PKHD1, and SHH were significantly upregulated (>1.5-fold) after CFI-400945 treatment, while ARL13B and PTCH1 were significantly downregulated in both cell lines. Taken together, our study suggests that PLK4 is involved in cilia loss in melanoma and its inhibition causes cilia reappearance and an anti-melanoma response. Further functional validation of these targets in PLK4-induced cilia loss in melanoma cells is currently ongoing in our laboratory. Minakshi Nihal^{1, 2}, Hao Chang^{2, 1}, Chandra K. Singh², Mary Ndiaye^{2, 1}, Nihal Ahmad^{2, 1} 1. Research, VA Medical Center Madison, Madison, WI, United States. 2. Dermatology, University of Wisconsin-Madison, Madison, WI, United States. Pigmentation, Melanoma, and Melanoma Immune Surveillance