Figure 3. p11 expression is regulated by A2.
A. HEK cells, which lack A2 and p11 expression, were transfected with hemaglutinin-tagged ubiquitin, with or without FLAG-tagged p11 and myc-tagged A2. Under these conditions, transfected FLAG-p11 was highly ubiquitinated and degraded in the proteasome (lane 2). The degree of ubiquitination of FLAG-p11 decreased, while total p11 expression increased, in response to incremental increases in A2 expression (lanes 3-6). Additional experiments revealed that A2 masks a polyubiquitination determinant on p11, protecting it from proteasomal destruction. B. In the endothelial cell, p11 can partner either with A2, promoting translocation of the heterotetramer to the cell surface, or with A2. If sufficient A2 is not present, p11 is ubiquitinated and destined for proteasomal destruction. Panel A reprinted with permission from (He et al., 2008).