The Tumor Suppressor RASSF1A and MAP-1 Link Death Receptor Signaling to Bax Conformational Change and Cell Death

Abstract

Tumor cells typically resist programmed cell death (apoptosis) induced by death receptors. Activated death receptors evoke Bax conformational change, cytochrome c release, and cell death. We report that the tumor suppressor gene RASSF1A is required for death receptor-induced Bax conformational change and apoptosis. TNFalpha or TRAIL stimulation induced recruitment of RASSF1A and MAP-1 to receptor complexes and promoted complex formation between RASSF1A and the BH3-like protein MAP-1. Normally, MAP-1 is inhibited by an intramolecular interaction. RASSF1A/MAP-1 binding relieved this inhibitory interaction, resulting in MAP-1 association with Bax. Deletion of the RASSF1A gene or short hairpin silencing of either RASSF1A or MAP-1 expression blocked MAP-1/Bax interaction, Bax conformational change and mitochondrial membrane insertion, cytochrome c release, and apoptosis in response to death receptors. Our findings identify RASSF1A and MAP-1 as important components between death receptors and the apoptotic machinery and reveal a potential link between tumor suppression and death receptor signaling.

Functional importance of RASSF1A microtubule localization and polymorphisms

“…MOAP-1 can associate with both wild type and the dMT mutant of RASSF1A in a time-dependent manner as previously observed (data now shown and Baksh et al, 2005). Similarly, RASSF1A self association was preserved in the dMT mutant of RASSF1A in a similar way to wild-type self association ( Figure 4a).…”

“…Detailed five-amino acid deletions revealed that the sequences 131 SQAEI and 300 ELHNFL were required for microtubule localization ( Figure 1b). It is interesting that 131 SQAEI is the ataxia telangeictasia mutated (ATM) phosphorylation site on RASSF1A (Agathanggelou et al, 2001) and 300 ELHNFL is just downstream of the site of association with the only known downstream effector of RASSF1A-mediated cell death, the modulator of apoptosis 1 (MOAP-1 at amino acid 311 REEEEHL) (Baksh et al, 2005;Foley et al, 2008). These results are similar to some of the published observations, which suggest that both N-and C-terminal regions of RASSF1A determine microtubule localization.…”

Mitochondria as therapeutic targets for cancer chemotherapy

“…This suggests a functional interaction between Bax and the CsAsensitive permeability transition pore complex (PTPC) (Marzo et al, 1998b;Belzacq et al, 2003). Another protein outside of the PTPC that may be required for Bax-mediated MOMP is the so-called modulator of apoptosis 1 (MAP-1) (Baksh et al, 2005;Tan et al, 2005).…”

Skp2 regulates the antiproliferative function of the tumor suppressor RASSF1A via ubiquitin-mediated degradation at the G1–S transition

“…Given that RASSF1A has a tumor suppressor function by inhibiting cell proliferation and survival (Dammann et al, 2000;Shivakumar et al, 2002;Song et al, 2004;Baksh et al, 2005), we thus examined whether Skp2 inhibits the tumor suppression function of RASSF1A. Overexpression of wild-type and S203A mutant forms of RASSF1A resulted in a significant loss of viability in U2OS cells (Figures 6a and b).…”

“…Furthermore, RASSF1A induces a G 1 arrest by engaging the Rb family G 1 -S checkpoint through inhibition of cyclin D1 (Shivakumar et al, 2002). RASSF1A is also involved in apoptosis by linking death receptor signaling to the apoptotic machinery (Baksh et al, 2005;Oh et al, 2006;Matallanas et al, 2007). However, the precise mechanism by which RASSF1A is regulated remains unclear.…”