Phosphoinositide 3‐kinase‐dependent activation of Rac

Welch, Heidi; Coadwell, W. John; Stephens, Len R.; Hawkins, Phillip T.

doi:10.1016/s0014-5793(03)00454-x

Cited by 291 publications

(257 citation statements)

References 54 publications

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“…Our data support previous findings that downstream of class I PI3K and PTEN, separable pathways preferentially control cell proliferation or tissue morphology [2,17,30,49]. We now show that HER2 overexpression can activate PI3K/AKT yet selectively drive proliferation in the absence of effects on tissue morphology.…”

Section: Discussionsupporting

confidence: 91%

Disruption of epithelial architecture caused by loss of PTEN or by oncogenic mutant p110α/PIK3CA but not by HER2 or mutant AKT1

et al. 2012

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Genetic changes in HER2, PTEN, PIK3CA and AKT1 are all common in breast cancer and lead to the elevated phosphorylation of downstream targets of the PI3K/AKT signalling pathway. Changes in HER2, PTEN, PIK3CA and AKT have all been reported to lead to both enhanced proliferation and failures in hollow lumen formation in three dimensional epithelial culture models, but it is not clear whether these failures in lumen formation are caused by any failure in the spatial coordination of lumen formation (hollowing) or purely a failure in the apoptosis and clearance of luminal cells (cavitation). Here we use NMuMG mammary epithelial cells, which form a hollow lumen without significant apoptosis, to compare the transformation by these four genetic changes. We find that either mutant PIK3CA expression or PTEN loss, but not mutant AKT1 E17K, cause disrupted epithelial architecture, whereas HER2 over-expression drives strong proliferation without affecting lumen formation in these cells. We also show that PTEN requires both lipid and protein phosphatase activity, its extreme C-terminal PDZ binding sequence and probably Myosin 5A to control lumen formation through a mechanism that does not correlate with its ability to control AKT, but which is selectively lost through mutation in some tumours. These findings correlate AKT independent signalling activated by mutant PIK3CA or PTEN loss, but not strongly by HER2, with disrupted epithelial architecture and tumour formation.

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Section: Discussionsupporting

confidence: 91%

Disruption of epithelial architecture caused by loss of PTEN or by oncogenic mutant p110α/PIK3CA but not by HER2 or mutant AKT1

et al. 2012

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“…Phosphatidylinositol 3-kinase (PI3K) may be an upstream activator of the Rac1-PLC-γ1-TonEBP/OREBP pathway. PI3K increases high NaCl-dependent transactivating activity of TonEBP/OREBP (33), and PI3K is known to activate Rac1 in other contexts (34). MKK6 (Fig.…”

Section: Discussionmentioning

confidence: 99%

Rac1/osmosensing scaffold for MEKK3 contributes via phospholipase C-γ1 to activation of the osmoprotective transcription factor NFAT5

Zhou

Yokoyama

Burg

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Separate reports that hypertonicity activates p38 via a Rac1-OSM-MEKK3-MKK3-p38 pathway and that p38α contributes to activation of TonEBP/OREBP led us to the hypothesis that Rac1 might activate TonEBP/OREBP via p38. The present studies examine that possibility. High NaCl is hypertonic. We find that siRNA knockdown of Rac1 reduces high NaCl-induced increase of TonEBP/OREBP transcriptional activity (by reducing its transactivating activity but not its nuclear localization). Similarly, siRNA knockdown of osmosensing scaffold for MEKK3 (OSM) also reduces high NaCl-dependent TonEBP/OREBP transcriptional and transactivating activities. Simultaneous siRNA knockdown of Rac1 and OSM is not additive in reduction of TonEBP/OREBP transcriptional activity, indicating a common pathway. However, siRNA knockdown of MKK3 does not reduce TonEBP/OREBP transcriptional activity, although siRNA knockdown of MKK6 does. Nevertheless, the effect of Rac1 on TonEBP/OREBP is also independent of MKK6 because it occurs in MKK6-null cells. Furthermore, we find that siRNA knockdown of Rac1 or OSM actually increases activity (phosphorylation) of p38, rather than decreasing it, as previously reported. Thus, the effect of Rac1 on TonEBP/OREBP is independent of p38. We find instead that phospholipase C-γ1 (PLC-γ1) is involved. When transfected into PLC-γ1-null mouse embryonic fibroblast cells, catalytically active Rac1 does not increase TonEBP/OREBP transcriptional activity unless PLC-γ1 is reconstituted. Similarly, dominant-negative Rac1 also does not inhibit TonEBP/OREBP in PLC-γ1-null cells unless PLC-γ1 is reconstituted. We conclude that Rac1/OSM supports TonEBP/ OREBP activity and that this activity is mediated via PLC-γ1, not p38. osmotic stress | MAPK H ypertonicity (e.g., high NaCl) activates the transcription factor TonEBP/OREBP (also known as NFAT5), resulting in increased expression of osmoprotective genes (1). Hypertonicity increases TonEBP/OREBP activity by increasing its abundance (1), transactivating activity (1), nuclear localization (1), and phosphorylation (2, 3). The regulatory increase of phosphorylation depends on both increased kinase activity and reduced phosphatase activity (4, 5). The stress-activated MAP kinase p38 has been extensively studied in this regard, but understanding its role has been complicated because hypertonicity activates two different p38s, namely p38α (MAPK14) and p38δ (MAPK13), which have opposite effects on TonEBP/OREBP activity: p38α increases TonEBP/OREBP activity and p38δ decreases it (6). Furthermore, the phosphospecific antibodies commonly used to measure p38 activity do not directly distinguish between p38α activity and p38δ activity, nor do some forms of inhibition that have been used (6). In this article, we will continue to refer to "p38" unless p38α and p38δ are distinguished. Hypertonicity activates p38α via the upstream kinase MKK3 (MAP2K3) or MKK6 (MAP2K6) (7), and p38α and MEKK3 (MAP3K3) contribute to hypertonicity-induced activation of TonEBP/OREBP (6, 8, 9). Thus, p38α contributes to To...

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“…Although the functional significance of this interaction is not clearly understood, p35/cdk5 is required for neurite outgrowth (110) and synaptic vesicle endocytosis (111), implicating a role for Rac1⅐GTP in both of these processes. Additionally, although it is well appreciated that phosphatidylinositides activate Rac1 through direct interaction with the PH domain of Rac1 GEFs, recent evidence has been presented that shows Rac1⅐GTP can positively regulate phosphatidylinositide production through its interaction with phosphatidylinositol 3-kinase (112). This suggests a potential role for alsin in the production of signaling lipids.…”

Section: Discussionmentioning

confidence: 99%

Alsin Is a Rab5 and Rac1 Guanine Nucleotide Exchange Factor

Topp

Gray

Gerard

et al. 2004

Journal of Biological Chemistry

173

157

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ALS2 is the gene mutated in a recessive juvenile form of amyotrophic lateral sclerosis (ALS2). ALS2 encodes a large protein termed alsin, which contains a number of predicted cell signaling and protein trafficking sequence motifs. To gain insight into the overall function of alsin and to begin to evaluate its role in motor neuron maintenance, we examined the subcellular localization of alsin and the biochemical activities associated with its individual subdomains. We found that the Vps9p domain of alsin has Rab5 guanine nucleotide exchange activity. In addition, alsin interacted specifically with and acted as a guanine nucleotide exchange factor for Rac1. Immunofluorescence and fractionation experiments in both fibroblasts and neurons revealed that alsin is a cytosolic protein, with a significant portion associated with small, punctate membrane structures. Many of these membrane structures also contained Rab5 or Rac1. Upon overexpression of full-length alsin, the overexpressed material was largely cytosolic, indicating that the association with membrane structures could be saturated. We also found that alsin was present in membrane ruffles and lamellipodia. These data suggest that alsin is involved in membrane transport events, potentially linking endocytic processes and actin cytoskeleton remodeling.Amyotrophic lateral sclerosis (ALS) 1 is a heterogeneous neurological disorder characterized by progressive degeneration of motor neurons, usually causing death as a result of respiratory paralysis (1, 2). Although mostly sporadic in nature, a genetic link has been established in 5-10% of ALS cases (3). Chromosomal mapping studies have identified six independent loci associated with the familial forms of ALS (Refs. 4 -10; reviewed in Refs. 11 and 12). Molecular genetic analysis identified two genes that, when mutated, lead to ALS. The first discovered was the gene coding for Cu-Zn superoxide dismutase 1 (SOD1) (10). Initially, mutations in SOD1 were thought to result in defective free radical scavenger activity. However, it is now generally accepted that the alterations in SOD1 that lead to ALS are the result of an unknown, but toxic gain-of-function. The second gene identified is mutated in a juvenile form of ALS, ALS2 (13,14). Mutations in this gene lead to a rare recessive form of ALS that presents early in life and progresses much more slowly than the classical form (6, 15). Two small deletions in ALS2 were originally associated with the disease (13,14). Each is expected to severely truncate the predicted protein product of ALS2. In addition, mutations in ALS2 have recently been associated with two other neurodegenerative disorders, juvenile-onset primary lateral sclerosis (14) and infantile-onset hereditary spastic paralegia (16 -18). Like the original mutations identified, these mutations are predicted to generate prematurely truncated forms of the protein product.The protein encoded by ALS2, alsin, is predicted to contain numerous domains implicating roles in cell signaling, membrane localization, and protein...

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Phosphoinositide 3‐kinase‐dependent activation of Rac

Cited by 291 publications

References 54 publications

Disruption of epithelial architecture caused by loss of PTEN or by oncogenic mutant p110α/PIK3CA but not by HER2 or mutant AKT1

Disruption of epithelial architecture caused by loss of PTEN or by oncogenic mutant p110α/PIK3CA but not by HER2 or mutant AKT1

Rac1/osmosensing scaffold for MEKK3 contributes via phospholipase C-γ1 to activation of the osmoprotective transcription factor NFAT5

Alsin Is a Rab5 and Rac1 Guanine Nucleotide Exchange Factor

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