Sumoylation is tumor-suppressive and confers proliferative quiescence to hematopoietic progenitors inDrosophila melanogasterlarvae

Abstract

Summary How cell-intrinsic regulation of the cell cycle and the extrinsic influence of the niche converge to provide proliferative quiescence, safeguard tissue integrity, and provide avenues to stop stem cells from giving rise to tumors is a major challenge in gene therapy and tissue engineering. We explore this question in sumoylation-deficient mutants of Drosophila. In wild type third instar larval lymph glands, a group of hematopoietic stem/progenitor cells acquires quiescence; a multicellular niche supports their undifferentiated state. However, how proliferative quiescence is instilled in this population is not understood. We show that Ubc9 protein is nuclear in this population. Loss of the SUMO-activating E1 enzyme, Aos1/Uba2, the conjugating E2 enzyme, Ubc9, or the E3 SUMO ligase, PIAS, results in a failure of progenitors to quiesce; progenitors become hyperplastic, misdifferentiate, and develop into microtumors that eventually detach from the dorsal vessel. Significantly, dysplasia and lethality of Ubc9 mutants are rescued when Ubc9wt is provided specifically in the progenitor populations, but not when it is provided in the niche or in the differentiated cortex. While normal progenitors express high levels of the Drosophila cyclin-dependent kinase inhibitor p21 homolog, Dacapo, the corresponding overgrown mutant population exhibits a marked reduction in Dacapo. Forced expression of either Dacapo or human p21 in progenitors shrinks this population. The selective expression of either protein in mutant progenitor cells, but not in other hematopoietic populations, limits overgrowth, blocks tumorogenesis, and restores organ integrity. We discuss an essential and complex role for sumoylation in preserving the hematopoietic progenitor states for stress response and in the context of normal development of the fly.

The EBF transcription factor Collier directly promotes Drosophila blood cell progenitor maintenance independently of the niche

“…3 B, E, and H). These phenotypes are in sharp contrast with that of Antp 17 /Antp 25 LG that do not present a marked increase in differentiation and uphold tepIV expression (Fig. 3 C, F, and I).…”

“…The transition from active proliferation (until the early L3 stage) to quiescence is associated with hemocyte differentiation (24,25), and signaling from the PSC was implicated in regulating blood cell quiescence (11). We thus assessed proliferation in early and late L3 LG (Fig.…”

“…3 C, F, and I). In fact, reminiscent of PSC-depleted LG, Antp 17 /Antp 25 LG harbored a normal proportion of tepIV + prohemocytes (Fig. S6), indicating that Antp is not required for prohemocyte maintenance.…”

ARF1–GTP regulates Asrij to provide endocytic control of Drosophila blood cell homeostasis

“…Supernumerary and hyperproliferated posterior lobes are seen in many cases where primary lobe hematopoiesis is perturbed. For example, sumoylation defective mutants like Ubc9 show posterior lymph gland tissue overgrowth (31). Pten mutants also display secondary lymph gland lobe overgrowth with numerous proliferating cells (22).…”

An extensive allelic series of Drosophila kae1 mutants reveals diverse and tissue-specific requirements for t6A biogenesis

“…For example, we and others previously characterized mutants of the central E1 and E2 enzymes in the SUMO pathway (the heterodimeric pair Aos1/Uba2 and Ubc9, respectively), and these develop a range of defects that are strikingly similar to what we documented for kae1 mutants. Phenotypes common to loss of Kae1 and SUMO include extended larval phases before lethality, presence of melanotic tumors, and preferential defects in mitotic versus nonproliferating cells, as evidenced by their lack of imaginal discs while retaining diverse other larval tissues (Kalamarz et al 2012;Kanakousaki and Gibson 2012). Similarly, a number of zygotic cell cycle mutants specifically abrogate development of imaginal discs while generally sparing other endoreplicated and post-mitotic larval tissues (Gatti and Baker 1989).…”