Galectin‐7 and actin are components of amyloid deposit of localized cutaneous amyloidosis

The precursor protein of localized cutaneous amyloidosis (LCA) is believed to be cytokeratins on the basis of previous immunohistochemical studies. To identify the candidate amyloid protein biochemically, amyloid proteins were extracted with distilled water from lesional skin of LCA associated with Bowen's disease. The proteins were resolved on one‐ or two‐dimensional polyacrylamide gel electrophoresis followed by characterization with immunoblot analysis. The proteins with multiple molecular weights of 50–67 kDa and two proteins with 25 and 35 kDa were identified as keratins, serum amyloid P component and apolipoprotein E, respectively. The unknown 14‐kDa (pI = 7.0) and 42‐kDa (pI = 5.4) proteins reacted with the antibody against galectin‐7 and actin, respectively. The protein with the molecular weight of 14 kDa was identified as galectin‐7 by MALDI‐TOF mass spectrometer. Their electrophoretic mobilities were identical with normal counterparts extracted from cultured normal human keratinocytes. Galectin‐7 and actin were detected by immunoblot assay in the water‐soluble fractions prepared from the lesional skins of two patients with primary LCA. Immunohistochemical studies of tumor‐associated (n = 9) and primary (n = 10) LCA revealed various degrees of positive immunoreactivities with the antibodies for galectin‐7 and F‐actin. Galectin‐7 and actin, which contain considerable amount of β‐sheet structure, may be candidate amyloidogenic proteins of primary and secondary LCA.