The Tumor Suppressor Gene hCDC4 Is Frequently Mutated in Human T-Cell Acute Lymphoblastic Leukemia with Functional Consequences for Notch Signaling

Abstract

Notch signaling is of crucial importance in normal T-cell development and Notch 1 is frequently mutated in T-cell acute lymphoblastic leukemias (T-ALL), leading to aberrantly high Notch signaling. In this report, we determine whether T-ALL mutations occur not only in Notch1 but also in the F-box protein hCdc4 (Sel-10, Ago, or Fbxw7), a negative regulator of Notch1. We show that the hCDC4 gene is mutated in leukemic cells from more than 30% of patients with pediatric T-ALL and derived cell lines. Most hCDC4 mutations found were missense substitutions at critical arginine residues (Arg 465 , Arg 479 , and Arg 505 ) localized in the substrate-binding region of hCdc4. Cells inactivated for hCdc4 and T-ALL cells containing hCDC4 mutations exhibited an increased Notch1 protein half-life, consistent with the proposed role of hCdc4 in ubiquitindependent proteolysis of Notch1. Furthermore, restoration of wild-type but not mutant hCdc4 in HCT 116 hCDC4-negative cells led to an increased Notch1 ubiquitylation and decreased Notch1 signaling. These results show that hCdc4 mutations interfere with normal Notch1 regulation in vivo. Finally, we found that mutations in hCDC4 and NOTCH1 can occur in the same cancers and that patients carrying hCDC4 and/or NOTCH1 mutations have a favorable overall survival. Collectively, these data show that mutation of hCDC4 is a frequent event in T-ALL and suggest that hCDC4 mutations and gainof-function mutations in NOTCH1 might synergize in contributing to the development of pediatric T-ALL leukemogenesis.

Triggering Fbw7-Mediated Proteasomal Degradation of c-Myc by Oridonin Induces Cell Growth Inhibition and Apoptosis

“…To further show the importance of Fbw7 in oridonininduced c-Myc degradation, we used 2 T-cell acute lymphoblastic leukemia (T-ALL) cell lines, Jurkat, and CCRF-CEM, which harbor an R505C and an R465C missense mutation in Fbw7, respectively (32,33). When exposed to oridonin, the decrease of c-Myc in these 2 cell lines was less evident than that in K562 (Fig.…”

FBXW7 is involved in Aurora B degradation

“…FBXW7 (F-box and WD repeat domain-containing 7) is one of the F-box proteins that function as substrate-recognition subunits of SCF complexes. Although SCF FBXW7 is known to regulate the degradation of several important substrates, such as Notch, c-Myc, cyclin E and c-Jun, 11,12 many of its substrates have yet to be identified. Importantly, FBXW7 is a tumor suppressor.…”

Regulation of APCCdh1 E3 ligase activity by the Fbw7/cyclin E signaling axis contributes to the tumor suppressor function of Fbw7

“…Characterized substrates of Fbw7 include cyclin E, c-Myc, c-Jun, and NOTCH-1, all of which are well-known products of oncogenes involved in a variety of human tumors [6,7,13]. Not surprisingly, Fbw7 is a tumor suppressor whose mutations occur in multiple neoplasms including breast cancer, colon cancer and leukemia [14][15][16][17][18]. Approximately 6% of all primary human tumors harbor mutations in the Fbw7 gene with the highest mutation rates found in cholangiocarcinoma and T-cell acute lymphoblastic leukemias (T-ALL) [7].…”

“…However, how Fbw7 suppresses tumor formation is currently not well understood. Although negative regulation of c-Myc and NOTCH-1 by Fbw7 has been implicated in tumorigenesis, their contributions to the tumor suppressor function of Fbw7 still require substantial characterization [16,[18][19][20]. On the other hand, cyclin E has garnered much attention as a possible key mediator for the ability of Fbw7 to inhibit tumorigenesis.…”