Silencing of Rab23 by siRNA inhibits ultraviolet B-induced melanogenesis via downregulation of PKA/CREB/MITF.

Recent investigations have shown that the Rab family of GTPases is associated with all aspects of melanogenesis. However, the effect of Rab23, which localizes to the plasma membrane and regulates the endocytic pathway within eukaryotic cells, in melanogenesis has not been reported. To understand the role of Rab23 in UVB-induced melanogenesis, we evaluated changes in the level of melanin, activity of tyrosinase and levels of melanogenesis-related proteins such as microphthalmia transcription factor and tyrosinase-related protein-1 (TRP-1) and the melanosome transport-related protein complex Rab27a-melanophilin-myosin Va after the downregulation of Rab23 in B16F10 and SK-MEL-2 cells with or without UVB irradiation. Our results showed that downregulating Rab23 reduced the melanin level and tyrosinase activity and inhibited the expression of proteins involved in UVB-induced melanogenesis. Rab23 colocalized with mature melanosomes marked with TRP-1. Furthermore, downregulating Rab23 induced the abnormal accumulation of melanosomes around the nucleus. We demonstrated that the downregulation of Rab23 inhibited melanin synthesis and melanosome transport by decreasing the PKA/CREB/MITF pathway, which is the key regulator of UVB-induced melanogenesis.

MicroRNA-340 is involved in ultraviolet B-induced pigmentation by regulating the MITF/TYRP1 axis.

OBJECTIVE: There is growing evidence that ultraviolet B (UVB) irradiation can change the expression profile of microRNAs (miRNAs) in immortalized human epidermal melanocytes (Pig-1). We aimed to investigate the effect of miR-340 on regulating UVB-induced pigmentation. METHODS: Real-time quantitative PCR (qRT-PCR) was used to evaluate the expression of miR-340 in Pig-1 cells. Immunoblotting analysis, qRT-PCR, and luciferase reporter assays were used to detect the potential target of miR-340. The sodium hydroxide dissolution assay was used to assess the effect of miR-340 on changes in melanin content. RESULTS: Expression of miR-340 was reduced in human Pig-1 cells after UVB irradiation. We found a negative correlation between miR-340 and melanocyte inducing transcription factor (MITF) in Pig-1 cells after UVB irradiation. Knockdown and overexpression of MITF in Pig-1 cells down- and upregulated melanogenesis, respectively. Overexpression of miR-340 inhibited MITF expression, reduced the amount of melanin, and suppressed expression of multiple key molecules involved in the pigment synthesis pathway, whereas knockdown of miR-340 showed the opposite results. CONCLUSIONS: Our results showed that miR-340 inhibited melanogenesis by regulating the downstream molecules of MITF and its signaling pathways, suggested that miRNA-340 may be a new target for the clinical treatment of UVB-induced pigmentation.

Lymphomatoid papulosis with folliculotropism, eccrinotropism and neurotropism.

The histopathological characteristics of lymphomatoid papulosis (LyP) vary. Currently, 6 subtypes have been reported, including a new subtype with perifollicular infiltration and different degrees of folliculotropism of CD30+ atypical lymphocytes, known as follicular LyP. However, LyP pathologically manifesting with folliculotropism, eccrinotropism and neurotropism has been rarely reported. We present a case of LyP showing CD30+ atypical lymphocytes around the hair follicle, eccrine gland and nerve fiber, with varying degrees of infiltrates. The pathological characteristics of folliculotropism and eccrinotropism are often associated with mycosis fungoides (MF). This case suggests that differential diagnosis is necessary when atypical lymphocytes infiltrate the follicle and eccrine gland. As folliculotropism and eccrinotropism can occur in both MF and LyP, it may represent a conceptual intersection between the 2 disease processes.