Sam68 Is Required for DNA Damage Responses via Regulating Poly(ADP-ribosyl)ation

Abstract

The rapid and robust synthesis of polymers of adenosine diphosphate (ADP)-ribose (PAR) chains, primarily catalyzed by poly(ADP-ribose) polymerase 1 (PARP1), is crucial for cellular responses to DNA damage. However, the precise mechanisms through which PARP1 is activated and PAR is robustly synthesized are not fully understood. Here, we identified Src-associated substrate during mitosis of 68 kDa (Sam68) as a novel signaling molecule in DNA damage responses (DDRs). In the absence of Sam68, DNA damage-triggered PAR production and PAR-dependent DNA repair signaling were dramatically diminished. With serial cellular and biochemical assays, we demonstrated that Sam68 is recruited to and significantly overlaps with PARP1 at DNA lesions and that the interaction between Sam68 and PARP1 is crucial for DNA damage-initiated and PARP1-conferred PAR production. Utilizing cell lines and knockout mice, we illustrated that Sam68-deleted cells and animals are hypersensitive to genotoxicity caused by DNA-damaging agents. Together, our findings suggest that Sam68 plays a crucial role in DDR via regulating DNA damage-initiated PAR production.

Sam68/KHDRBS1-dependent NF-κB activation confers radioprotection to the colon epithelium in γ-irradiated mice

“…We recently revealed that Sam68 plays a crucial role in controlling DNA damage-induced PARP1 activation and PAR production; hence Sam68 deficiency dramatically dampens the PAR-dependent NF-κB signaling and DNA repair pathways initiated by DNA damage (Fu et al, 2016; Sun et al, 2016). As a key early signaling regulator that converges at the proxy of the DNA damage-triggered signaling cascade in the nucleus, Sam68 could provide a novel target for cancer therapeutics.…”

“…Whole-body γ-irradiation (WBIR) in mice was performed as previously described (Sun et al, 2016). The γ-irradiated mice were sacrificed at indicated time points post WBIR for the indicated analyses, and the mortality and survival of mice were also monitored post γ-irradiation.…”

Sam68 is required for the growth and survival of nonmelanoma skin cancer

“…We recently reported that Sam68 is an important early DNA damage signaling molecule that regulates DNA damage‐induced activation of poly(ADP‐ribose) polymerase 1 (PARP1) thus fulfilling an essential function in DNA repair and NF‐κB activation signaling pathways . As tumor cells generally acquire enhanced DNA repair activities to overcome the intrinsic DNA damage that frequently occurs during rapid proliferation, we sought to examine whether elevated levels of Sam68 in NMSC are essential for the cellular responses to DNA damage.…”

“…γ‐Irradiation of A431 cells and immortalized keratinocytes was performed using a 137 Cesium source (dose rate 8 Gy/min) as previously described …”

“…Whether DDR plays an important role in the development and survival of NMSC and whether it could be therapeutically targeted in NMSC remain largely unknown. Our recent studies reveal that Src‐associated substrate during mitosis of 68 kDa (Sam68) is an early‐onset and key effector of the response to DNA damage . Elevated expression of Sam68 occurs in multiple types of cancers and also correlates with tumor progression .…”