Activation of the Rb/E2F1 Pathway by the Nonproliferative p38 MAPK during Fas (APO1/CD95)-mediated Neuronal Apoptosis

Abstract

Aberrant activation of the Rb/E2F1 pathway in cycling cells, in response to mitogenic or nonmitogenic stress signals, leads to apoptosis through hyperphosphorylation of Rb. To test whether in postmitotic neurons the Rb/E2F1 pathway can be activated by the nonmitogenic stress signaling, we examined the role of the p38 stress-activated protein kinase (SAPK) in regulating Rb phosphorylation in response to Fas (CD95/APO1)-mediated apoptosis of cultured cerebellar granule neurons (CGNs). Anti-Fas antibody induced a dramatic and early activation of p38. Activated p38 was correlated with the induction of hyperphosphorylation of both endogenous and exogenous Rb. The p38-selective inhibitor, SB203580, attenuated such an increase in pRb phosphorylation and significantly protected CGNs from Fas-induced apoptosis. The cyclin-dependent kinase-mediated Rb phosphorylation played a lesser role in this neuronal death paradigm, since cyclin-dependent kinase inhibitors, such as olomoucine, roscovitine, and flavopiridol, did not significantly prevent anti-Fas antibody-evoked neuronal apoptosis. Hyperphosphorylation of Rb by p38 SAPK resulted in the release of Rb-bound E2F1. Increased E2F1 modulated neuronal apoptosis, since E2F1؊/؊ CGNs were significantly less susceptible to Fas-mediated apoptosis in comparison with the wildtype CGNs. Taken together, these studies demonstrate that neuronal Rb/E2F1 is modulated by the nonproliferative p38 SAPK in Fas-mediated neuronal apoptosis.

Gadd45b Mediates Fas-induced Apoptosis by Enhancing the Interaction between p38 and Retinoblastoma Tumor Suppressor

“…The p38-induced hyperphosphorylation of Rb is one of the mechanisms of Fas-induced apoptosis (3,4), and Gadd45b participates in TGF-␤-induced apoptosis by activating p38 in AML12 cells (14). To examine the susceptibility of AML12 cells to the Fas antibody Jo2, cells were analyzed by TUNEL staining and cell death detection ELISA analysis.…”

“…Alternatively, Fas also can activate the p38 MAPK 2 pathway through an adaptor protein, Daxx. p38 has been shown to inactivate Rb by hyperphosphorylation and to release free E2F1 to induce some proapoptotic genes or repress other antiapoptotic genes during Fas-induced apoptosis (3,4). The Gadd45 (growth arrest and DNA damage-inducible, 45) family proteins include three closely related members (a, b, and g) whose transcription is induced by a variety of genotoxic stresses as well as by terminal differentiation and apoptotic cytokines (5-7).…”

p38 MAPK as a negative regulator of VEGF/VEGFR2 signaling pathway in serum deprived human SK-N-SH neuroblastoma cells

“…This discrepancy in the levels of caspase activity may reflect why caspase-3/7 activation but not caspase-3 cleavage is observed in untreated and SB202190 serum starved treated cells. It is conceivable that p38 MAPK regulates caspase-3 activation through caspase-8 directly [3], death receptor activation [8] or the translocation of the proapoptotic protein Bax to the mitochondria [6]. Alternatively, the p38 MAPK-independent mechanism may involve a direct activation of caspase-7 by caspase-9 [19], calpain [23], granzyme B or cathepsin G [29] to function independently of caspase-3.…”

“…Whereas growth factors stimulate the ERK1/2 cascade to regulate cellular processes such as proliferation, differentiation and survival, stressful stimuli stimulate the p38 MAPK pathway to induce cell death [15]. In neuronal cells, p38 MAPK pathway is linked to caspase activation and apoptosis induced by glutamate, β-amyloid, dopamine, 6-hydroxydopamine and cell death receptor activation [3,8,11,12,30]. Moreover, a blockade of p38 MAPK signaling can also provide neuroprotection in vivo [2,4,28].…”

Pocket proteins and cell cycle control

“…Here, pRB appeared to be phosphorylated by p38MAPK on residues distinct from those targeted by Cdks (Wang et al, 1999;Nath et al, 2003). This p38-dependent pRB phosphorylation resulted in the release of E2F1 and is implicated in Fasinduced apoptosis (Hou et al, 2002).…”