The block of adipocyte differentiation by a C-terminally truncated, but not by full-length, simian virus 40 large tumor antigen is dependent on an intact retinoblastoma susceptibility protein family binding domain

Abstract

Simian virus 40 (SV40) can promote cell transformation and suppress differentiation. It does this partly by targeting tumor suppressors such as p53 and members of the retinoblastoma susceptibility protein (Rb) family. This work concentrates on mechanisms by which SV40 large tumor antigen (SVLT) suppresses adipocyte differentiation. We created cell lines derived from murine 3T3-L1 preadipocytes expressing different versions of SV40 early-region sequences. SVLT-expressing cells failed to exhibit adipocyte morphology, to induce glycerophosphate dehydrogenase activity, and to induce differentiation-dependent mRNA for adipocyte P2. SVLT alone was sufficient, in the absence of SV40 small tumor antigen, to inhibit differentiation. A truncated SVLT containing only the N-terminal 121 amino acids (SVLT1-121) blocked differentiation, thus mapping at least one differentiation blocking function to the N-terminal region. K1 (Glu-1073Lys) point mutants of SVLT, which are unable to bind to the Rb protein family or induce neoplastic transformation, are defective for blocking differentiation in the case of SVLT1-121 but retain the ability to block differentiation in the case of full-length SVLT. This finding demonstrates that Rb family proteins are important in regulating adipocyte differentiation but that other functions of full-length SVLT can block adipocyte differentiation independently of RB family binding and transformation.

Rb and p107 regulate preadipocyte differentiation into white versus brown fat through repression of PGC-1α

“…The Rb family of proteins play an important role in regulating adipocyte differentiation (Altiok et al, 1997;Chen et al, 1996;Cherington et al, 1988;Fajas et al, 2002b;Hansen et al, 2004aHansen et al, , 1999Hansen et al, , 2004bHiggins et al, 1996;May et al, 2001;290 CELL METABOLISM : NOVEMBER 2005 Porse et al, 2001;Reichert and Eick, 1999;Richon et al, 1997;Slomiany et al, 2000). Our experiments demonstrate that p107 is required for white adipocyte differentiation in vivo and suggest that this lack of differentiation is a result of an inability to appropriately regulate pRb.…”

“…Sequestration of Rb family members by SV40 large T antigen inhibits adipocyte differentiation (Cherington et al, 1988;Higgins et al, 1996). Antisense suppression of p107 inhibits adipocyte differentiation of a preadipocyte cell line (May et al, 2001).…”

p107 Is a Crucial Regulator for Determining the Adipocyte Lineage Fate Choices of Stem Cells

“…However, unlike p107, Rb functions during adipogenesis and for the maintenance of the terminally differentiated state rather than commitment of stem cells. In accordance with this idea is the finding that simian virus 40 (SV40) antigen that inactivates Rb results in the inhibition of adipogenesis in committed white preadipocyte cells . In addition, Rb‐deficient fibroblasts are unable to differentiate into white adipocytes .…”

Intricate Transcriptional Networks of Classical Brown and Beige Fat Cells

“…Consistent with this, mesenchymal progenitor-specific Rb KO embryos show a significant increase in classical BAT mass ( 63 ). Intriguingly, while Rb is required for white adipocyte differentiation in vitro ( 64 , 65 ), adipose-specific KO of Rb ( 66 ) or inactivation of Rb via SV40 T antigen in WAT ( 67 ) results in browning of WAT. Expression of p107 is abundant in the SVF from Vis WAT, lower in subQ WAT, and absent in BAT ( 68 ).…”