8848

TSC22D1

Ptg-2|TGFB1I4|TSC22;TSC22 domain family, member 1;TSC22D1;TSC22 domain family, member 1

TGFB-stimulated clone 22 homolog|TGFbeta-stimulated clone 22|TSC22 domain family protein 1|cerebral protein 2|regulatory protein TSC-22|transcriptional regulator TSC-22|transforming growth factor beta-1-induced transcript 4 protein|transforming growth fac

13q14

protein-coding

Tsc-22 is a novel tumor suppressor gene that represents a new class of transcription factors that has transcriptional repressor activity. We found Tsc-22 downregulation in livers from B6C3F1 mice following treatment for 2 weeks with carcinogenic doses of the antianxiety drug oxazepam (2500 ppm) or the peroxisome proliferator Wyeth-14,643 (500 ppm) but not with two other carcinogens such as o-nitrotoluene or methyleugenol or three noncarcinogens including p-nitrotoluene, eugenol, or acetaminophen. The expression of Tsc-22 was also repressed in B6C3F1 mouse liver tumors that were induced by several chemicals from 2-year carcinogenicity studies as well as in spontaneous liver tumors. To identify potential Tsc-22 target genes in mouse liver, we transfected small interference RNA (SiRNA) designed to inhibit Tsc-22 into murine liver BNL-CL.2 cells. We selected two potential transcriptional targets of Tsc-22, growth arrest and DNA damage-inducible gene 45 beta (Gadd45b) and leucine zipper, putative tumor suppressor 2 (Lzts2) to test based on our previous complementary DNA microarray studies, showing that expression of these cancer-associated genes was increased when Tsc-22 was repressed. SiRNA treatment of BNL-CL.2 cells with Tsc-22 oligonucleotides but not nonspecific oligonucleotides decreased RNA and protein expression of Tsc-22 by 80-90%, while expression of Gadd45b gene, but not Lzts2, was increased over time after an initial decrease. Treatment of these cells with oxazepam for 48 h also resulted in decreased Tsc-22 and increased Gadd45b expression. These data provide evidence that Tsc-22 is a suppressor of Gadd45b expression, which may contribute to an early antiapoptotic response.

Transforming growth factor-beta (TGF-beta)-stimulated clone-22 (TSC-22) was originally isolated as a TGF-beta-inducible gene. In this study, we identified TSC-22 as a potential leukemia suppressor. Two types of FMS-like tyrosine kinase-3 (Flt3) mutations are frequently found in acute myeloid leukemia: Flt3-ITD harboring an internal tandem duplication in the juxtamembrane domain associated with poor prognosis and Flt3-TKD harboring a point mutation in the kinase domain. Comparison of gene expression profiles between Flt3-ITD- and Flt3-TKD-transduced Ba/F3 cells revealed that constitutive activation of Flt3 by Flt3-TKD, but not Flt3-ITD, upregulated the expression of TSC-22. Importantly, treatment with an Flt3 inhibitor PKC412 or an Flt3 small interfering RNA decreased the expression level of TSC-22 in Flt3-TKD-transduced cells. Forced expression of TSC-22 suppressed the growth and accelerated the differentiation of several leukemia cell lines into monocytes, in particular, in combination with differentiation-inducing reagents. On the other hand, a dominant-negative form of TSC-22 accelerated the growth of Flt3-TKD-transduced 32Dcl.3 cells. Collectively, these results suggest that TSC-22 is a possible target of leukemia therapy.

Aberrant methylation of tumor suppressor genes can lead to their silencing in many cancers. TSC-22 is a gene silenced in several solid tumors, but its function and the mechanism(s) responsible for its silencing are largely unknown. Here we demonstrate that the TSC-22 promoter is methylated in primary mouse T or natural killer (NK) large granular lymphocyte (LGL) leukemia and this is associated with down-regulation or silencing of TSC-22 expression. The TSC-22 deregulation was reversed in vivo by a 5-aza-2-deoxycytidine therapy of T or NK LGL leukemia, which significantly increased survival of the mice bearing this disease. Ectopic expression of TSC-22 in mouse leukemia or lymphoma cell lines resulted in delayed in vivo tumor formation. Targeted disruption of TSC-22 in wild-type mice enhanced proliferation and in vivo repopulation efficiency of hematopoietic precursor cells (HPCs). Collectively, our data suggest that TSC-22 normally contributes to the regulation of HPC function and is a putative tumor suppressor gene that is hypermethylated and silenced in T or NK LGL leukemia.