Human PARP1 adenoviral particles

High-mobility group box 1 protein (HMGB1) exhibits various functions depending on its subcellular localization and is finely regulated by multiple post-translational modifications, such as acetylation. HMGB1 in the nucleus protects against cardiac hypertrophy, while its exogenous protein has been shown to induce hypertrophic responses. This study investigated the regulatory relationship between poly (ADP-ribose) polymerase 1 (PARP1) and HMGB1 during pathological cardiac hypertrophy. Primary cultured neonatal rat cardiomyocytes (NRCMs) were incubated with three cardiac hypertrophy stimuli, including angiotensin II (Ang II), phenylephrine (PE), and isoproterenol (ISO), and cell surface area and mRNA expression of hypertrophy biomarkers were measured. The catalytic activity of PARP1 was significantly enhanced, while HMGB1 was excluded from the nucleus. PARP1 overexpression by infecting with adenovirus PARP1 (Ad-PARP1) can promote the export of HMGB1 to the nucleus and promote its secretion outside the cell, aggravating cardiac hypertrophy, while HMGB1 overexpression can alleviate this phenomenon. PE treatment can produce similar effects, while PARP1 silencing or its specific inhibitor AG14361 can significantly inhibit this effect. These studies provide new evidence that PARP1 binds to HMGB1 and accelerates its translocation from the nucleus to the cytoplasm, ultimately leading to cardiac hypertrophy.

To determine whether there is an interaction between PARP1 and HMGB1, the researchers first performed co-immunoprecipitation (co-IP) experiments using NRCMs. As shown in Figure 1a, b, PARP1 protein was precipitated with anti-PARP1 antibody, followed by Western blot analysis. Under Ad-PARP1 adenovirus infection conditions, the binding of PARP1 to HMGB1 was significantly enhanced (Figure 1a). However, PE treatment weakened the binding of PARP1 to HMGB1 (Figure 1b). PARP1 was consistently observed in the precipitate collected by anti-HMGB1 antibody (Figure 1c, d). After Ad-PARP1 infection, the interaction between PARP1 and HMGB1 was significantly enhanced (Figure 1c). However, this interaction was reduced by PE incubation (Figure 1d). In addition, IF experiments also observed intracellular colocalization of PARP1 and HMGB1 in NRCMs (Figure 1e). In addition, Ad-PARP1 increased the PARylation of HMGB1, while the PARylation level was inhibited after PE exposure (Figure 1f). These results suggest that PARP1 interacts with and PARylates HMGB1 in the nucleus of NRCMs.

Figure 1. The interaction between PARP1 and HMGB1 in the nucleus of NRCMs. (Li Q, et al., 2019)