Four and a half LIM protein 1C (FHL1C)

Four-and-a-half LIM domain protein 1 isoform A (FHL1A) is
predominantly expressed in skeletal and cardiac muscle. Mutations
in the FHL1 gene are causative for several types of hereditary
myopathies including X-linked myopathy with postural muscle atrophy
(XMPMA). We here studied myoblasts from XMPMA patients. We found
that functional FHL1A protein is completely absent in patient
myoblasts. In parallel, expression of FHL1C is either unaffected or
increased. Furthermore, a decreased proliferation rate of XMPMA
myoblasts compared to controls was observed but an increased number
of XMPMA myoblasts was found in the G(0)/G(1) phase. Furthermore,
low expression of K(v1.5), a voltage-gated potassium channel known
to alter myoblast proliferation during the G(1) phase and to
control repolarization of action potential, was detected. In order
to substantiate a possible relation between K(v1.5) and FHL1C, a
pull-down assay was performed. A physical and direct interaction of
both proteins was observed in vitro. In addition, confocal
microscopy revealed substantial colocalization of FHL1C and K(v1.5)
within atrial cells, supporting a possible interaction between both
proteins in vivo. Two-electrode voltage clamp experiments
demonstrated that coexpression of K(v1.5) with FHL1C in Xenopus
laevis oocytes markedly reduced K(+) currents when compared to
oocytes expressing K(v1.5) only. We here present the first evidence
on a biological relevance of FHL1C.