The parafibromin tumor suppressor protein interacts with actin-binding proteins actinin-2 and actinin-3.
BACKGROUND
Germline and somatic inactivating mutations in the HRPT2 gene occur in the inherited hyperparathyroidism-jaw tumor syndrome, in some cases of parathyroid cancer and in some cases of familial hyperparathyroidism. HRPT2 encodes parafibromin. To identify parafibromin interacting proteins we used the yeast two-hybrid system for screening a heart cDNA library with parafibromin as the bait.


RESULTS
Fourteen parafibromin interaction positive preys representing 10 independent clones encoding actinin-2 were isolated. Parafibromin interacted with muscle alpha-actinins (actinin-2 and actinin-3), but not with non-muscle alpha-actinins (actinin-1 and actinin-4). The parafibromin-actinin interaction was verified by yeast two-hybrid, GST pull-down, and co-immunoprecipitation. Yeast two-hybrid analysis revealed that the N-terminal region of parafibromin interacted with actinins. In actin sedimentation assays parafibromin did not dissociate skeletal muscle actinins from actin filaments, but interestingly, parafibromin could also bundle/cross-link actin filaments. Parafibromin was predominantly nuclear in undifferentiated proliferating myoblasts (C2C12 cells), but in differentiated C2C12 myotubes parafibromin co-localized with actinins in the cytoplasmic compartment.


CONCLUSIONS
These data support a possible contribution of parafibromin outside the nucleus through its interaction with actinins and actin bundling/cross-linking. These data also suggest that actinins (and actin) participate in sequestering parafibromin in the cytoplasmic compartment.
Agarwal
Sunita K
SK
National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, Maryland, USA. sunitaa@mail.nih.gov
Simonds
William F
WF
Marx
Stephen J
SJ
D000185:Actinin / Q000378:metabolism*; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015723:Gene Library; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D010282:Parathyroid Neoplasms / Q000378:metabolism; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
C401401:ACTN2 protein, human; C118456:ACTN3 protein, human; C454900:CDC73 protein, human; D025521:Tumor Suppressor Proteins; D000185:Actinin