NAC1, an actin-binding BTB/POZ protein in cancer cell cytokinesis and murine vertebral patterning

Nucleus accumbens-associated protein I (NAC1) is a member of the BTB (Bric-a-Brac Tramtrack Broad complex) family of proteins. Recent studies have demonstrated that NAC1 expression is essential for sustaining cancer cell proliferation and migration, but its molecular mechanisms remain elusive. In my dissertation project, I show that NAC1 is an actin monomer binding protein with a Kd of 0.78 muM, and the BTB domain is the binding domain. Disrupting NAC1 protein complex function by expressing a dominant-negative protein or by RNA interference resulted in reduced traction and incomplete abscission during late stage cytokinesis leading to multi-nucleation of cancer cells. In Nac1-/- mouse fibroblasts, re-expression of NAC1 from a retroviral vector was sufficient to partially avert multi-nucleation. Furthermore, the silencing of profilin-1 in cancer cells caused a similar multi-nucleation phenotype, and NAC1 modulated protein interaction between actin and profillin-1. Next, I examined the phenotype of Nac I knockout mice, and discovered the loss of Nac 1 protein expression led to a patterning defect in the vertebral skeletal axis. The majority of Nac 1-null mice exhibited morphological transformation of the sixth lumbar vertebra into a sacral identity; a decreased total number of pre-sacral vertebrae elements from 26 in wild type mice to 25. Immunohistochemistry found strong Nacl expression in the chondrocytes of the murine and human cartilaginous tissues. Genetic knockout of Nac I significantly reduces the migratory potential of murine chondrocytes. In light of its interaction with the actin cytoskeleton, NAC1 could play an important role in the migratory capacity of cancer cells and mesenchyme cells. These findings highlight the potential of NAC1 as a molecular target to inhibit cancer pathogenesis.