KIF5A de novo mutation associated with myoclonic seizures and neonatal onset progressive leukoencephalopathy.

The KIF5A gene (OMIM 602821) encodes a neuron-specific kinesin heavy chain involved in intracellular transport of mitochondria and other cargoes. KIF5A protein comprises the N terminal motor domain, the stalk domain and the C-terminal cargo binding domain. The binding between KIF5A and its cargoes is mediated by kinesin adaptor proteins such as TRAK1 and TRAK2. Numerous missense KIF5A mutations in the motor and stalk domains cause spastic paraplegia type 10 (SPG10, OMIM 604187). Conversely, the role of loss-of-function mutations, especially those affecting the cargo binding domain, is unclear. We describe a novel de novo KIF5A p.Ser974fs/c.2921delC mutation found by whole exome sequencing in a patient with a congenital severe disease characterized by myoclonic seizures and progressive leukoencephalopathy. Since this phenotype differs considerably from the KIF5A/SPG10 disease spectrum we propose that the KIF5A p.Ser974fs and possibly other mutations which lead to truncation of the C-terminal tail of the protein cause a novel disorder. We speculate that the unique effect of the C-terminal truncating KIF5A mutations may result from the previously described complex role of this protein domain in binding of the TRAK2 and possibly other kinesin adaptor protein(s).

Unfaithfulness and promiscuity of a mutant androgen receptor in a hormone-refractory prostate cancer.

Missense mutations in the androgen receptor (AR) contribute to the failure of hormonal therapy for prostate cancer (PCa), but the underlying molecular bases remain uncharacterized. Here, we describe a new AR variant found in a hormone-refractory metastatic PCa, in which threonine 575 in the DNA binding domain, and threonine 877 in the ligand-binding domain, were both replaced by an alanine. Using gene reporter assays, we demonstrate that the T575A mutation weakened transcriptional activity from promoters containing AR-specific responsive elements, while activity from promoters with AR-non-specific elements was enhanced. Data from gel shift experiments revealed a preferential binding of the T575A mutant to AR-non-specific motifs. We demonstrate that the two mutations T575A and T877A cooperate to confer new functional properties on the AR, and that the mutant AR functions simultaneously as a promiscuous AR due to the T877A mutation, and an unfaithful AR due to the T575A mutation.