The Role of a Ubiquitin Processing Protease in the Growth‐to‐Development Transition of Dictyostelium Development

The ubiquitin processing protease, UbpA (a homolog of human IsoT), is required for multicellular development of Dictyostelium. ubpA − cells are unable to respond to starvation and make the growth‐to‐development transition. In addition, we show that ubpA − cells were hypersensitive to oxidative and nitrosative stresses, and grew to a much lower cell density than parental cells before entering stationary phase. Although pulses of exogenous cAMP allows ubpA − cells to aggregate, overexpression of acaA (adenylyl cyclase) does not rescue the developmental defect. Interestingly, UbpA is required for the growth‐stage expression of lmcB , which is involved in sensing nutrient levels and signaling cells to develop upon starvation. Overexpression of lmcB partially rescues the defect in ubpA − cells. To elucidate LmcB‐dependent pathways and characterize their regulation by UbpA, we have identified interacting partners of LmcB. Preliminary results indicate that LmcB interacts with the ubiquitinated form of a cAMP‐inducible protein. These results will lead to a better understanding of the mechanisms cells use to sense starvation stress and respond by making the transition from growth to development.