Oxygen-responsive p53 tetramer-octamer switch controls cell fate

Abstract

12Solid tumors require an efficient decision-making mechanism to progress 13 through a gradient of hypoxia. Here, we show that an oxygen-sensory p53 14 tetramer-octamer switch makes cell decision for survival or death in variable 15 hypoxia. Trapping homo-oligomers from biosynthesis cycle, we found a 16 metastable p53 tetramer in cells. Under the operation of switch, tetramer 17 segregates the p53 character of a tumor suppressor and promoter. The p53 18 switch generates a pattern of its on-off state in time that is specific to the 19 strength of hypoxia. A bidirectional tetramer-octamer conversion in on state 20 decides the restoration of basal state by forward and programs apoptosis 21 upon the reverse shift via p53-MDM2 loop. However, reversible dimer-22 tetramer transitions in off state trigger chaperoning of HIF-1 complex by 23 tetramer in forward and oncogenic gain-of-function by prion-like dimers in 24 reverse direction. Temporal on-off patterns calibrate stabilized p53 pool by 25 defining the abundance of dimer, tetramer and octamer that ultimately 26 decides diverse cellular outcomes in hypoxia. Through multi-chromophore 27 FRET, we further show that chaperoning of HIF-1 may modulate angiogenesis 28 through a possible flip-flop of the p53T-HIF-1 complex upon DNA. Our results 29 demonstrate how p53 can sense oxygen and act upon its homo-30 oligomerization states to control cell fate in hypoxic tumors. 31 33 part of specific gene expression in DNA damage repair, cell cycle arrest, apoptosis and 34senescence, has led to propose multiple mechanisms (1). p53 is inactive with loss of its 35 apoptotic potential in the hypoxic region of solid tumors (2) and it remains unknown 36 whether p53 transforms this state in order to control tumorigenesis through a gradient of 37 oxygen. Variable tissue oxygenation in solid tumor triggers p53 conformational 38 transitions from wild-type (WT) to mutant-like (ML) states, or vice versa, in order to 39 control cancer progression (3) and it further modulates post-translational modifications 40 2 in myocardial infarction dictating survival or death of the cell (4). Besides, change in ROS 41 levels differentially controls p53 post-translational modifications in controlling p53-42 mediated apoptosis and necrosis (5). However, the mechanism of p53's varied dynamics 43 under oxygen stress is unknown. The cellular events operate through chemical 44 switchboards, gene-protein loops and protein circuits in response to external stimuli. 45Molecular switches such as bacterial iron-cluster protein that senses molecular oxygen, 46 iron, nitric oxide in countering to changing circumstances (6), GTP-binding between the 47 GDP-bound off and the GTP-bound on state (7,8) and ion-mediated conformational 48 switches and switchable lipids reversibly shifting between two or more stable states in 49 response to stimuli and in microenvironment have been reported (9,10). Protein Tox, a 50 decisive molecular switch for exhaustion mode of immune cells, activates a genetic 51 program that alters immun...

Oxygen-generated spatial distribution of cell population links to p53 status

“…Under fluctuating oxygen, SP and CP tend to maintain diminished and enhanced cytoplasmic to nuclear p53 distribution ratio respectively which might result in mislocalization of WT or MT p53 and transformation of cell fate upon SP⇄CP transitions. Enhanced survival of WT p53 cells in a wide range of oxygen variation justifies the significance of such spatial dynamics in selecting WT p53 for oxygen-sensitive responses (14) (Fig 3B).…”

“…The experimental procedure was performed as described previously (14). Cells were grown on coverslips and exposed to different conditions of oxygen.…”

“…It is known that a gradient of low oxygen selects for p53 mutant-like phenotypes and affects p53’s status of a tumor suppressor by diverse mechanisms (9–13). Recently, we have shown WT p53 as a cellular oxygen sensor that operates through the tetramer→octamer switch in its homo-oligomerization system and controls survival or death in a gradient of hypoxia (14). We asked how the same gradient selects or maintains WT p53 phenotypes in a heterogeneous cancer cell population.…”