The Ca2+-dependent protease Calpain A regulates Cactus/IκB levels during Drosophila development in response to maternal Dpp signals

Abstract

Regulation of NF kappaB activity is central to many processes during development and disease. Activation of NF kappaB family members depends on degradation of inhibitory I kappaB proteins. In Drosophila, a nuclear gradient of the NF kappaB/c-rel protein Dorsal subdivides the embryonic dorsal-ventral axis, defining the extent and location of mesodermal and ectodermal territories. Activation of the Toll pathway directs Dorsal nuclear translocation by inducing proteosomal degradation of the I kappaB homologue Cactus. Another mechanism that impacts on Dorsal activation involves the Toll-independent pathway, which regulates constitutive Cactus degradation. We have shown that the BMP protein Decapentaplegic (Dpp) inhibits Cactus degradation independent of Toll. Here we report on a novel element of this pathway: the calcium-dependent protease Calpain A. Calpain A knockdowns increase Cactus levels, shifting the Dorsal gradient and dorsal-ventral patterning. As shown for mammalian I kappaB, this effect requires PEST sequences in the Cactus C-terminus, implying a conserved role for calpains. Alteration of Calpain A or dpp results in similar effects on Dorsal target genes. Epistatic analysis confirms Calpain A activity is regulated by Dpp, indicating that Dpp signals increase Cactus levels through Calpain A inhibition, thereby interfering with Dorsal activation. This mechanism may allow coordination of Toll, BMP and Ca(2+) signals, conferring precision to Dorsal-target expression domains.

Calpain A modulates Toll responses by limited Cactus/IκB proteolysis

“…The shape of the gradient is also altered at 15% e.l., although the amplitude is not reduced as at 50% e.l. (Figure 4, G, H, K, and L). These alterations are consistent with the decrease in twist and snail domains, as well as with modifications in the size of lateral neuroectodermal territories previously reported (Fontenele et al ., 2009, and data not shown). Of importance, basal (dorsal region) Dl levels are unaltered at any position under CalpA KD, unlike the reduction seen by lowering the dose of the dl gene (Figure 4, I and J).…”

“…CalpA-V5 is present in the cytosol; however, particulate distribution of CalpA-V5 is also observed (Figure 1, F and G). This may correspond to inner plasma membrane localization of CalpA, in agreement with enrichment of CalpA in the submembranous domain during embryogenesis (Emori and Saigo, 1994; Fontenele et al. , 2009).…”

“…CalpA protein is apically enriched in the submembranous cytoplasm of the embryo syncytium (Emori and Saigo, 1994; Fontenele et al. , 2009).…”

“…, 2009). In cact loss-of-function mutants apical restriction is lost (Figure 5, A and B; Fontenele et al ., 2009), whereas in cact [E10] mutants CalpA is distributed as patches close to the membrane (Figure 5, C and I) and does not redistribute during mitosis (Figure 5, D and J). In both conditions calpain activity, measured with a fluorescent substrate, is decreased (Figure 5E).…”

αPS1βPS integrin receptors regulate the differential distribution of Sog fragments in polarized epithelia

“…Maternal Dpp has a role in patterning the dorsal-ventral axis of the embryo. The embryonic phenotypes observed as a result of follicle cell Integrin clones closely resemble phenotypes reported for alterations of the maternal Dpp pathway (Carneiro et al, 2006;Fontenele et al, 2009). Thus, Integrins may impact Dpp function during early embryogenesis by regulating Sog distribution in the perivitelline space.…”