Drosophila p53 isoforms differentially regulate apoptosis and apoptosis-induced proliferation

Abstract

Irradiated or injured cells enter apoptosis, and in turn, promote proliferation of surrounding unaffected cells. In Drosophila, apoptotic cells have an active role in proliferation, where the caspase Dronc and p53 induce mitogen expression and growth in the surrounding tissues. The Drosophila p53 gene structure is conserved and encodes at least two protein isoforms: a full-length isoform (Dp53) and an N-terminally truncated isoform (DΔNp53). Historically, DΔNp53 was the first p53 isoform identified and was thought to be responsible for all p53 biological activities. It was shown that DΔNp53 induces apoptosis by inducing the expression of IAP antagonists, such as Reaper. Here we investigated the roles of Dp53 and DΔNp53 in apoptosis and apoptosis-induced proliferation. We found that both isoforms were capable of activating apoptosis, but that they each induced distinct IAP antagonists. Expression of DΔNp53 induced Wingless (Wg) expression and enhanced proliferation in both 'undead cells' and in 'genuine' apoptotic cells. In contrast to DΔNp53, Dp53 did not induce Wg expression in the absence of the endogenous p53 gene. Thus, we propose that DΔNp53 is the main isoform that regulates apoptosis-induced proliferation. Understanding the roles of Drosophila p53 isoforms in apoptosis and in apoptosis-induced proliferation may shed new light on the roles of p53 isoforms in humans, with important implications in cancer biology

The function of Drosophila p53 isoforms in apoptosis

“…We first examined the protein expression levels of p53 protein isoforms by western blotting using an antibody raised against the human p53 C-terminus, which is conserved in all Drosophila isoforms. 41,42 Western blotting of wild-type larval brain and imaginal disc (B-D) extracts revealed an~48 kDa band, close to the predicted size of the 43.7 kDa p53A protein isoform, that was not detected in extracts from p53 5A-1-4 null mutants, consistent with previous results from our lab and others ( Figure 5a, lanes 1, 2). 16,41,42 The predicted p53B (55.6 kDa) and p53D/E (~36-38 kDa) isoforms were not detected, although all lanes had a non-specific 72 kDa band (Figure 5a).…”

“…The p53B isoform may also participate in other processes that Drosophila p53 has been implicated in, which include the culling of primordial germ cells, meiotic checkpoints, DNA repair, stem cell divisions, and tissue regeneration. 41,[60][61][62][63][64][65][66][67][68][69] Our results indicate that p53A and p53B localize to nuclear bodies and physically associate, an interaction that is likely direct through the conserved p53 oligomerization domain. Therefore, p53 tetramers may be heterogeneous and have different ratios of p53A and p53B subunits.…”

“…The well-studied p53A isoform is also known as ΔNp53 because it is 110 amino acid (AA) shorter in its N-terminal TAD than the longest 56 kD p53B isoform (Figure 1a). 16,41 Previous evidence indicated that p53B can induce apoptosis when overexpressed, but the normal physiological function of p53B has not been evaluated. 41,42 Two shorter isoforms have also been predicted by RNA-Seq.…”

“…16,41 Previous evidence indicated that p53B can induce apoptosis when overexpressed, but the normal physiological function of p53B has not been evaluated. 41,42 Two shorter isoforms have also been predicted by RNA-Seq. The p53E mRNA isoform appeared in the annotated genome in the year 2014 and predicts a 334 AA (~38 kD) protein (Figures 1a and b).…”

Expression of dengue virus NS3 protein inDrosophilaalters its susceptibility to infection

“…22 Briefly, wandering third instar larvae were dissected using inside-out technique directly in PBS. Tissues were fixed in 4% formaldehyde in PBS 20 min at room temperature with mild agitation.…”