PIAS4 SUMOylates PARP1 at lysine-203 and lysine-486 with SUMO2,3 in response to heat shock (Martin et al. 2009, Lamoliatte et al. 2013, Hendriks et al. 2014, Tammsalu et al. 2014). PARP1 reciprocally poly(ADP-ribose)ylates PIAS4 (Martin et al. 2009). SUMOylation of PARP1 is required for full activation of the HSP70.1 promoter (Martin et al. 2009).