An essential cytoskeletal linker protein connecting actin microfilaments to intermediate filaments

Neurofilament subunit NF-H modulates axonal diameter by selectively slowing neurofilament transport

To examine the mechanism through which neurofilaments regulate the caliber of myelinated axons and to test how aberrant accumulations of neurofilaments cause motor neuron disease, mice have been constructed that express wild-type mouse NF-H up to 4.5 times the normal level. Small increases in NF-H expression lead to increased total neurofilament content and larger myelinated axons, whereas larger increases in NF-H decrease total neurofilament content and strongly inhibit radial growth. Increasing NF-H expression selectively slow neurofilament transport into and along axons, resulting in severe perikaryal accumulation of neurofilaments and proximal axonal swellings in motor neurons. Unlike the situation in transgenic mice expressing modest levels of human NF-H (Cote, F., J.F. Collard, and J.P. Julien. 1993. Cell. 73:35-46), even 4.5 times the normal level of wild-type mouse NF-H does not result in any overt phenotype or enhanced motor neuron degeneration or loss. Rather, motor neurons are extraordinarily tolerant of wild-type murine NF-H, whereas wild-type human NF-H, which differs from the mouse homolog at > 160 residue positions, mediates motor neuron disease in mice by acting as an aberrant, mutant subunit.

The integrin alpha 6 beta 4 and the biology of carcinoma

The integrin family of adhesion receptors plays a major role in epithelial organization and function. Moreover, the altered expression and function of specific integrins most likely contributes significantly to carcinoma progression. The integrin alpha 6 beta 4, the focus of this review, is a receptor for several members of the laminin family and is preferentially expressed at the basal surface of most epithelia, where it contributes to basement membrane interactions. Mounting evidence suggests that the alpha 6 beta 4 integrin plays a key role in carcinoma cell biology. Several histopathological studies have established a correlation between alpha 6 beta 4 integrin expression and tumor progression. The importance of alpha 6 beta 4 expression in tumors in underscored by the findings that invading fronts of several carcinomas are enriched in the expression of alpha 6 beta 4 integrin ligands, such as laminin-1 and laminin-5. The participation of the alpha 6 beta 4 integrin in invasion is supported further by in vitro functional studies using carcinoma cells that have been transfected with the beta 4 cDNA. The mechanisms by which alpha 6 beta 4 contributes to tumor progression are probably related to its mechanical and signaling properties and are currently under intense study.