Cell invasion occurs naturally during development; however, it also contributes to tumor progression. Although understudied, data from different cancer subtypes suggests that a dichotomy exists between invasive and proliferative behavior. Our lab uses the C. elegans anchor cell (AC) to study this proliferative-invasive switch during uterine-vulval development. Post-embryonically, the AC invades into the vulval epithelium to form the mature vulva. We have shown that the AC exists in G0/G1-cell cycle arrest during invasion, which requires the nuclear hormone transcription factor, nhr-67 (tailless/Tlx). Loss of nhr-67 results in mitotic, non-invasive ACs. nhr-67 maintains AC arrest by regulating the expression of the cyclin-dependent kinase inhibitor, cki-1 (p21/p27). Induced expression of CKI-1 is sufficient to restore invasion in an nhr-67-depleted background, suggesting that the G1/G0 state is required for invasive activity. Differentiation of invasive behavior is also regulated by chromatin modifiers that act downstream and/or parallel to G0/G1 arrest. We have found that the histone deacetylase, hda-1, promotes AC invasion by positively regulating pro-invasive gene expression; however, whether hda-1 regulates invasion by controlling cell cycle arrest is unknown. We and others have recently shown that key pro-invasive transcription factors, nhr-67/Tlx, hlh-2/E, fos-1a/Fos, and egl-43/Evi1, maintain the AC in a post-mitotic, pro-invasive state by acting as part of gene regulatory network composed of two subcircuits. nhr-67, egl-43, and hlh-2 function in a type 1 coherent loop with positive feedback to maintain the AC in a post-mitotic state and facilitate invasion, while fos-1 acts in a cell cycle-independent subcircuit to promote invasion. Using genetic approaches, CRISPR-Cas9 genome engineering and high-resolution imaging, we explored the regulatory relationships between HDA-1 and these key transcription factors. We find that hda-1 functions in the AC to maintain G1/G0 arrest, and that loss and depletion of hda-1 results in mitotic, non-invasive ACs. We show that in the AC, hda-1 regulates the activity of NHR-67, FOS-1a, and HLH-2. Interestingly, induced expression of CKI-1 fails to restore invasion in hda-1-deficient ACs, but is able to rescue the mitotic defect of hda-1-depleted animals. These results suggest that hda-1 functions in both cell cycle-dependent and independent subcircuits to maintain the post-mitotic, pro-invasive state of the AC.

Authors: Palmisano, Nicholas, Martinez, Michael A. Q., Medwig-Kinney, Taylor, Moore, Frances E. Q., Saldanha, Joanne, Sirota, Sydney S., Smith, Jayson, Zhang, Wan, Matus, David Q.

Affiliation:
- Stony Brook University