Werner Zwerschke

To better understand the significance of local insulin-like growth factor-binding protein 3 (IGFBP-3) in the development of osteosarcoma, IGFBP-3 levels and subcellular localization were compared in biopsies from osteosarcomas and unaffected normal bone tissues. IGFBP-3 levels were analyzed by immunohistochemistry in 21 osteosarcomas and 5 unaffected bone tissues. IGFBP-3 levels were compared for patient outcome. Mature osteocytes of normal bone tissues contained high levels of predominantly nuclear IGFBP-3, whereas only 50% of osteosarcomas contained IGFBP-3-positive tumor cells, with predominantly cytoplasmic IGFBP-3 staining. Comparison of IGFBP-3 levels for patient outcome resulted in two groups. Patients with a low level of IGFBP-3 in osteosarcoma experienced a trend for a shorter survival time than did patients with a high level of IGFBP-3. Our results suggest that the levels and subcellular localization of local IGFBP-3 play a role in osteosarcoma development. Further prospective evaluation with higher clinical sample numbers might reveal a prognostic role for IGFBP-3 level in local tumors in patients with osteosarcoma.

Pyruvate kinase M2 (M2‐PK) controls the rate‐limiting step at the end of the glycolytic pathway in normal proliferating and tumor cells. Other functions of M2‐PK in addition to its role in glycolysis are little understood. The aim of this study was to identify new cellular interaction partners of M2‐PK in order to discover novel links between M2‐PK and cellular functions. Here we show that the SUMO‐E3 ligase protein PIAS3 (inhibitor of activated STAT3) physically interacts with M2‐PK and its isoenzyme M1‐PK. Moreover, we demonstrate that endogenous SUMO‐1‐M2‐PK conjugates exist in mammalian cells. Furthermore, we show that transient expression of PIAS3 but not the RING domain mutant PIAS3 (C299S, H301A) is consistent with nuclear localization of M2‐PK and PIAS3 and M2‐PK partially co‐localize in the nucleus of these cells. This study suggests a link between PIAS3 and nuclear pyruvate kinase. J. Cell. Biochem. 107: 293–302, 2009.

Tumor cells express the glycolytic regulator pyruvate kinase subtype M2 (M2‐PK), which can occur in a tetrameric form with high affinity to its substrate phosphoenolpyruvate (PEP) and a dimeric form with a low PEP affinity. The transition between both conformations contributes to the control of glycolysis and is important for tumor cell proliferation and survival. Here we targeted M2‐PK by synthetic peptide aptamers, which specifically bind to M2‐PK and shift the isoenzyme into its low affinity dimeric conformation. The aptamer‐induced dimerization and inactivation of M2‐PK led to a significant decrease in the PK mass‐action ratio as well as ATP:ADP ratio in the target cells. Furthermore, the expression of M2‐PK‐binding peptide aptamers moderately reduced the growth of immortalized NIH3T3 cell populations by decelerating cell proliferation, but without affecting apoptotic cell death. Moreover, the M2‐PK‐binding peptide aptamers also reduced the proliferation rate of human U‐2 OS osteosarcoma cells. In the present study, we developed the first specific inhibitors of the pyruvate kinase isoenzyme type M2 and present evidence that these inhibitors moderately decelerate tumor cell proliferation.