Multiple death pathways in retina-derived 661W cells following growth factor deprivation: crosstalk between caspases and calpains

Abstract

During development of the mammalian retina, neurons that do not succeed in establishing functional synaptic connections are eliminated by apoptosis, allowing the formation of a finely tuned network. Growth factors play a crucial role in controlling the balance between apoptosis and survival signals not only at developmental stages but also in longterm preservation of retinal functions. In the present work, we explore the apoptotic mechanisms triggered by growth factor deprivation of retina-derived 661W cells. Under serum starvation conditions, these cone photoreceptors underwent cell death with participation of caspase-9, -3 and -12. Interestingly, inhibition of caspases did not prevent apoptosis but only resulted in a temporary delay. We show m-calpain activation in parallel with caspases, indicating that more than one execution pathway is available to cone photoreceptors. Moreover, crosstalk of the caspase and calpain pathways was detected, suggesting a loop that may act to amplify the apoptotic cascade.

Insulin Receptor Signaling in Cones

“…To further substantiate the existence of the IR signaling pathway in cone photoreceptors, we analyzed lysates of 661W cells (a cone-like transformed cell line) for expression of IR and its downstream effectors by immunoblotting analysis. This cell line has previously been used to study the multiple death pathways in cone photoreceptors (50). The results indicate that 661W cells express almost all IR signaling proteins.…”

Redox survival signalling in retina-derived 661W cells

“…Elevated cytosolic Ca 2 þ also plays a role in photoreceptor apoptosis. 25,26 Analysis of intracellular Ca 2 þ using Fluo3-AM (fluo-3-acetoxymethyl ester) showed a shift in the fluorescence peak after 2-h treatment, indicating an increase in the levels of free cytoplasmic Ca 2 þ (Figure 3c). Overall, these results demonstrate that early apoptotic events are detectable following the decline in the H 2 O 2 burst.…”

Novel Mechanisms of Target Cell Death and Survival and of Therapeutic Action of IVIg in Pemphigus

“…Binding of PVIgGs from both subgroups activated caspase 9, which may provide a common step in death signaling pathway downstream of both the calpain-and the caspase 8-mediated events. 60,61 A slightly less pronounced up-regulation of caspase 9 in keratinocytes treated with the PVIgG predominantly activating the calpain-mediated pathway may be explained by an ability of calpain to cleave caspase 9 by calpain, generating the inactive form of this caspase. 62 Upstream of the apoptosis and oncosis effectors, autoantibodies from two different PV patients preferentially activated distinct signaling mechanisms.…”