Activation of the Ran GTPase Is Subject to Growth Factor Regulation and Can Give Rise to Cellular Transformation

Abstract

Although the small GTPase Ran is best known for its roles in nucleocytoplasmic transport, mitotic spindle assembly, and nuclear envelope formation, recent studies have demonstrated the overexpression of Ran in multiple tumor types and that its expression is correlated with a poor patient prognosis, providing evidence for the importance of this GTPase in cell growth regulation. Here we show that Ran is subject to growth factor regulation by demonstrating that it is activated in a serum-dependent manner in human breast cancer cells and, in particular, in response to heregulin, a growth factor that activates the Neu/ ErbB2 tyrosine kinase. The heregulin-dependent activation of Ran requires mTOR (mammalian target of rapamycin) and stimulates the capped RNA binding capability of the cap-binding complex in the nucleus, thus influencing gene expression at the level of mRNA processing. We further demonstrate that the excessive activation of Ran has important consequences for cell growth by showing that a novel, activated Ran mutant is sufficient to transform NIH-3T3 cells in an mTOR-and epidermal growth factor receptor-dependent manner and that Ran-transformed cells form tumors in mice.Ran is a unique member of the Ras superfamily of GTPases that utilizes a guanine nucleotide exchange factor (the chromatin-associated RCC1 protein), a GTPase-accelerating protein complex (RanGAP/RanBP1), and a single major class of effectors (the importins or karyopherins) to regulate the nucleocytoplasmic transport of various cargo as well as other nuclear functions (for review, see Ref. 1). In interphase cells, a Ran-GTP gradient is formed in response to the nuclear localization of RCC1 together with the cytoplasmic localization of RanGAP. As a result, Ran exists predominantly in an active, GTP-bound state in the nucleus where it is capable of engaging its primary biological effectors, the importins/karyopherins. GTP hydrolysis, catalyzed by RanGAP in the cytoplasm, then results in the dissociation of Ran-GDP from its effector proteins. The nucleocytoplasmic transport of a number of proteins is dependent upon the proper establishment of the Ran-GTP gradient, as best exemplified in the case of classical nuclear import (2). Protein cargo destined for the nucleus is identified by the presence of a nuclear localization sequence. The nuclear localization sequence is recognized by an adapter protein, importin-␣, in the cytosol, and upon binding the cargo, importin-␣ engages importin-␤ to form a complete import complex that translocates to the nucleus. Within the nucleus, Ran-GTP binds to importin-␤, causing it to dissociate from the import complex, which results in the subsequent release of cargo. Thus, the fact that Ran-GTP is predominantly a nuclear species is pivotal in the directional release of import cargo into the nucleus.Similarly, it has been suggested that Ran plays an essential role in the directional release of capped RNAs in the cytoplasm by regulating the interactions that occur between the nuclear cap-binding complex (CBC) 2 ...

Nano-encapsulation of a novel anti-Ran-GTPase peptide for blockade of regulator of chromosome condensation 1 (RCC1) function in MDA-MB-231 breast cancer cells

“…Therefore, an awareness and understanding of target pathways is essential to the development of novel therapeutics. Specifically, recent studies show that Ran (Ras-related nuclear) protein is involved in growth regulation, apoptotic resistance, tumour transformation, increased aggressiveness and enhanced metastasis in a wide range of tumour types, such as breast, and is, therefore, a potential therapeutic target (Abe et al, 2008;Kurisetty et al, 2008;Ly et al, 2010;Xia et al, 2008;Yuen et al, 2012).…”

High nuclear karyopherin α 2 expression is a strong and independent predictor of biochemical recurrence in prostate cancer patients treated by radical prostatectomy

“…Evidence for the latter hypothesis comes from the established functional relationship between PTEN deletion and increased PI3K/AKT signaling, 47 which has been shown to enhance both the activity and capacity of the nucleocytoplasmic transportation machinery. 48,49 The existence of rearrangements involving alternative ETS family members in 'fusion-type' prostate cancer, which are undetectable by ERG IHC, offers an alternative explanation for the strong association of PTEN loss with KPNA2 expression in ERGnegative cancers. PTEN deletions are known to be very tightly linked to ERG-positive cancer.…”

Nuclear Translocation of Type I Transforming Growth Factor β Receptor Confers a Novel Function in RNA Processing

“…The ALK5(D266A)/HA and ALK5(3A)/HA constructs were kindly provided by Peter ten Dijke (Leiden University Medical Center, Netherlands) and are described elsewhere (23). The Ran(WT), Ran(F35A), and Ran(T24N) constructs (25) were kindly provided by Richard Cerione (Cornell University). Recombinant human TGF-␤1 was purchased from R&D Systems (Minneapolis, MN).…”