sites for several transcription factors, including Sp1 and PROX1, is located
at position −110 bp of the PKCβ promoter (Fig. 1C). Basal expression of
PKCβ is controlled by two Sp1-binding sites and adjacent prosperorelated
homeobox 1 (PROX1) binding sites. The potential role of methylation
in regulating PKCβ expression was recently reported. Hagiwara
et al. showed that treatment with a demethylating agent, 5-aza-2′-
deoxycytidine, restored PKCβ mRNA expression in PROX1-expressing
cells [31] and identified a CpG island in the corresponding region of
DNA, in particular one CpG site that overlapped with the distal Sp1 site.
Hypermethylation of the PROX1 sites inhibited Sp1 binding to this region.
Finally, a previous study identified a repressor region located upstream
of -110 bp in the PKCβ promoter, but the nuclear factor(s) that bind to
this region have not yet been characterized [32]. This implicates an
auto-feedback loop in the production of PKCβ that is mediated through
a PKCβ-responsive site and may lead to an overshoot phenomenon in
the induction of PKCβ in adipose tissue of HFD-fed mice.