139. THE REGULATION OF TRP53 IN SPERM

Abstract

TRP53 is a tumour suppressor protein that is a universal sensor of cell stress. Upon ejaculation, sperm undergo a process of capacitation which allows them to become fertile. We have previously shown that mouse and human sperm possess TRP53. In this study we analyzed the regulation TRP53 presence in sperm. Mouse sperm were collected from the epididymides and incubated for various times in fertilisation medium. TRP53 was detected by both Western blot analysis and immunolocalization. We found that sperm collected directly from the epididymis generally had little or no detectable TRP53. The level increased with time in culture over a period of 120 min. Most of the TRP53 was detected in the midpiece of sperm although it was also detected in the head of a small proportion of sperm. The increase in TRP53 with time accompanied the increase in the proportion of sperm undergoing the acrosome reaction. Yet, Trp53-null sperm still underwent the acrosome reaction at a normal rate. By contrast, sperm that were prevented from undergoing capacitation and the acrosome reaction (by the removal of albumin or calcium from media) showed a marked reduction in the amount of TRP53 detected. This shows that TRP53 may be dependent upon capacitation, but the reverse was not the case. Inhibition of protein synthesis by puromycin did not block the time-dependent increase in TRP53 in sperm. Canonically, the TRP53 level is controlled by its rate of degradation by MDM2-ubiquitin mediated proteolysis. We found that MDM2 was present in sperm and inhibition of MDM2 (by Nutlin-3) caused an acute increase in TRP53 detected in sperm. This study shows that TRP53 levels are acutely regulated in sperm during the time that sperm acquire the capacity to fertilise, yet sperm lacking TRP53 are capable of fertility. Identification of the role for this TRP53 in sperm is under investigation.