Validation and Functional Characterization of Novel Neurofibromin Interacting Proteins

Neurofibromin (NF1) is a 2,818aa protein encoded by the very large NF1 tumour suppressor gene located on chromosome 17q11.2. Loss of function mutations and deletions in NF1 underlie Neurofibromatosis type-1 (NF-1) - the most common inherited syndrome of the nervous system in humans with a birth incidence of 1:3,000. The most visible feature of NF-1 is the neoplastic manifestations known as neurofibromas, however, the syndrome is also characterized by pigmentary defects, peripheral motor dysfunction, learning disabilities and several developmental abnormalities. The molecular etiology of many of these non-neoplastic phenotypes remains unknown. Here we demonstrate that the Tubulin Binding Domain (TBD) of NF1 is a binding partner of the Leucine Rich Pentatrico Peptide Repeat motif-Containing protein (LRPPRC) and cytoplasmic Dynein Heavy Chain (DHC). The NF1-LRPPRC interaction is of high significance as it links NF-1 with Leigh’s Syndrome, French Canadian variant (LSFC) – an autosomal recessive neurodegenerative disorder that arises due to mutations in the LRPPRC gene. This interaction occurs as part of an RNA granule complex, and use of transgenic mouse models establishes an important role of NF1 and LRPPRC in peripheral nerve development. The NF1-DHC interaction is of importance in melanocytes where our studies suggest a possible role in melanosome localization, disruptions in which may underlie the abnormal pigmentary features known as café-au-lait macules that are commonly associated with NF-1. The validation of LRPPRC and DHC as novel NF1 interactors reveal new roles of NF1, which open the door to better understanding the molecular mechanisms that underlie the myriad of NF-1 manifestations.Ph