Nuclear accumulation and up-regulation of p53 and its associated proteins after H2S treatment in human lung fibroblasts

recent years, it has become clear that hydrogen sulphide (H2S) plays a number of biological roles and may function as a novel gasotransmitter in the body alongside nitric oxide (NO) and carbon monoxide (CO) [1]. H2S is synthesized naturally from L-cysteine in mammalian tissues in a reaction catalysed by two enzymes, cys-tathionine-␥-lyase (CSE) and cystathionine-␤-synthetase (CBS) [2]. Recently, attention has been focused on the potential physiological and pathophysiological role of H2S in the body. It has been shown, for example, H2S plays a role in the regulation of vascular function both in health and disease [3–5]. Interestingly, H2S is also produced naturally at sites of inflammation and it is known that chronic inflammation is associated with uncontrolled cellular proliferation. However, in contrast to other gasotransmitter (e.g. NO) very little information exists on the mechanism by which H2S influences cell growth. In the present study, we have attempted to assess the biological effects of H2S in normal human lung fibrob-last (MRC-5) cells. Recently, we have reported that H2S treatment increased cell death, formation of micronuclei (MN) and alteration in cell cycle [6]. Broadly, similar conclusions were also reported using single cell gel electrophoresis (SCGE) to show that sodium sulphide (Na2S: 250 ␮M/L) caused radical-associated DNA damage in the Chinese hamster ovary (CHO) cells [7]. Together, these data indicate that H2S is a potent clastogenic agent and suggest that it has a role in DNA damage-induced responses. In the present study, we have intended to understand the mechanism(s) involved in the genomic instability caused by H2S. The tumour suppressor protein p53 plays a key role in maintaining genomic integrity by controlling cell-cycle progression and cell survival [8]. Cells under stresses such as DNA damage, hypoxia and aberrant oncogene signals trigger the tumour suppressor protein p53, which transcribes genes that induce cell-cycle arrest, DNA repair and apoptosis [8, 9]. The mechanisms by which H2S up-regulates p53 and thereby induces DNA damage and alters cell-cycle progression remain unclear. In the present study, we report that the up-regulation of both the inducer protein p53 and the effector protein p21 in normal lung fibroblast cells several hours after 50 ␮M of NaHS (donor of H2S) treatment followed by the key proteins involved in cell cycle, i.e. Cyclin A, Cyclin E (a trend for CDC-6, p16 to increase) and decrease in Cyclin D, with a trend for p27 to decline (Fig. 1A). Interestingly, down-regulation of p27 and …