Transforming growth factor‐β‐stimulated clone‐22 is a negative‐feedback regulator of Ras / Raf signaling: Implications for tumorigenesis

Abstract

Transforming growth factor-b (TGF-b)-stimulated clone-22 (TSC-22), also called TSC22D1-2, is a putative tumor suppressor. We previously identified TSC-22 downstream of an active mutant of fms-like tyrosine kinase-3 (Flt3). Here, we show that TSC-22 works as a tumor suppressor through inhibiting Ras ⁄ Raf signaling. Notably, TSC-22 was upregulated by Ras ⁄ Raf activation, whereas its upregulation was inhibited by concurrent STAT5 activation. Although TSC-22 was normally retained in the cytoplasm by its nuclear export signal (NES), Ras ⁄ Raf activation caused nuclear translocation of TSC-22, but not TSC22D1-1. Unlike glucocorticoidinduced leucine zipper (GILZ ⁄ TSC22D3-2) previously characterized as a negative regulator of Ras ⁄ Raf signaling, TSC-22 failed to interact physically with Ras ⁄ Raf. Importantly, transduction with TSC-22, but not TSC22D1-1, suppressed the growth, transformation and tumorigenesis of NIH3T3 cells expressing oncogenic H-Ras: this suppression was enhanced by transduction with a TSC-22 mutant lacking NES that had accumulated in the nucleus. Collectively, upregulation and nuclear translocation of TSC-22 played an important role in the feedback suppression of Ras ⁄ Raf signaling. Consistently, TSC22D1-deficient mice were susceptible to tumorigenesis in a mouse model of chemically-induced liver tumors bearing active mutations of Ras ⁄ Raf. Thus, TSC-22 negatively regulated Ras ⁄ Raf signaling through a mechanism different from GILZ, implicating TSC-22 as a novel suppressor of oncogenic Ras ⁄ Raf-induced tumors. (Cancer Sci 2012; 103: 26-33) T he gene encoding transforming growth factor b (TGF-b)-stimulated clone-22 (TSC-22) was originally isolated as a TGF-b-inducible gene.(1) The TSC-22 domain (TSC22D) family of leucine zipper protein includes TSC22D1, TSC22D2, TSC22D3 and TSC22D4. TSC-22, also called TSC22D1-2, is a short isoform of TSC22D1 including two splice variants, whereas TSC22D1-1 is a long splice variant.(2-4) Glucocorticoid-induced leucine zipper (GILZ), also called TSC22D3-2, is a splice variant of TSC22D3.(4-7) TSC-22 contains a nuclear export signal (NES) at the N-terminus, followed by a TSC-box and a leucine zipper motif. (2,3,8,9) TSC-22 homodimerizes or heterodimerizes with other transcription factors.(10) Forced expression of TSC-22 induces growth suppression, apoptosis or differentiation in several tumor ⁄ leukemia cell lines. (11)(12)(13)(14) Interestingly, expression of TSC-22 was downregulated in several cancers. (15)(16)(17) In addition, TSC-22 was epigenetically silenced in large granular lymphocyte leukemia. (14) In contrast, TSC-22 was upregulated by many different stimuli.(1,2) However, the mechanism underlying the transcriptional upregulation of TSC-22 has remained obscure. We recently reported that TSC-22 was upregulated by an active mutant of FMS-like tyrosine kinase-3 (Flt3) harboring a point mutation in the kinase domain (Flt3-TKD).(13) In contrast, a Flt3 active mutant harboring an internal tandem duplication in the juxtamembrane domain (Flt3-ITD) did not s...

Les protéines de la famille TSC-22D

“…Sont indiqués les différents gènes de la famille TSC-22D, les transcrits, les protéines (les plus étudiées en gras), ainsi que la taille des ARNm et des protéines. l'apoptose ou après activation de la voie Ras/Raf [14,15]. Notre équipe a mis en évidence la localisation cytoplasmique de GILZ dans des cellules hématopoïétiques, et identifié une séquence NES (nuclear export signal) dans sa région amino-terminale, sans toutefois que la fonctionnalité de cette séquence n'ait été formellement démontrée [16].…”

“…Récemment, une interaction directe entre GILZ et SMAD2 été décrite dans les lymphocytes T (LT) [13]. Enfin, une séquence fonctionnelle NES (nuclear export signal) a été identifiée dans la région amino-terminale de TSC-22, expliquant sa localisation cytoplasmique [14]. TSC-22 migre dans le noyau lors de …”

“…Le rôle de TSC-22 TSC-22 inhibe la prolifération cellulaire de lignées hématopoïétiques ou issues de carcinomes en bloquant la progression du cycle cellulaire [14,28]. Ainsi, dans la lignée de carcinome colique Moser S, TSC-22 induit la transcription du gène codant pour p21 (cyclin-dependent kinase inhibitor 1), bloquant ainsi les cellules en phase G0/G1 [9].…”

“…Ainsi, dans la lignée de carcinome colique Moser S, TSC-22 induit la transcription du gène codant pour p21 (cyclin-dependent kinase inhibitor 1), bloquant ainsi les cellules en phase G0/G1 [9]. TSC-22 inhibe aussi la prolifération cellulaire induite par la voie de signalisation Ras/Raf, sans interagir avec Ras, comme décrit pour GILZ [14].…”

Study of the correlation between H-ras mutation and primary hepatocellular carcinoma

“…The exact mechanism remains unknown. Certain studies have reported the levels of growth factors, including transforming growth factor-β (TGF-β) and fibroblast growth factor (bFGF), enhanced DNA synthesis and anchorage-dependent growth in cells with H-ras mutation (12,13). Furthermore, H-ras mutation caused progressive tumors in nude mice; however, those tumors were distinct from v-ras-induced tumors, indicating that H-ras mutation was directly involved in cell growth and transformation and the development of tumors (14).…”