Microarray analysis of microRNA expression in cutaneous squamous cell carcinoma

MicroRNAs (miRNAs) are a novel class of short RNAs which have shown to be dysregulated in a variety of cancers including squamous cell carcinoma (SCC) of the head&neck. Microarray based miRNA expression profiles of cutaneous SCC (cSCC) however have not been investigated so far. Seven patients with cutaneous SCC were enrolled in the study. Tumor biopsies (n=7) were taken from the center of the tumor. Adjacent healthy skin (n=7) was biopsied as a control (intraindividual control). miRNA expression profiles of all specimen were detected by mircroarray miRNA expression profiling based on miRBAse 16 and compared. In 7 patients biopsy specimens of cutaneous SCC and control specimens from an adjacent healthy skin site near the tumor border (intraindividual control) were obtained during surgical removal of the tumor. Specimes were immediately stored in RNAlater (Qiagen, HIlden, Germany) at -80 °C. Total RNA including miRNAs were isolated with miRNeasy Mini Kit (Quiagen, Hilden, Germany) according to the manufacturer’s protocol. For RNA quality control purposes we determined RNA concentration, purity and RNA integrity number (RIN) with Agilent 2100 Bioanalyzer, RNA 6000 NanoLabCHip Kits (both Agilent Technologies, Santa Clara, USA) and the NanoDrop ND-1000 spectral photometer (Peqlab, Erlangen, Germany). All of the following steps described were carried out according to the manufacturer´s protocol. In order to enable assessment of labeling and hybridization efficiencies total RNA samples were spiked with MicroRNA Spike-In Kit (Agilent Technologies, Santa Clara, USA). After treatment with calf intestine phosphatase (CIP), a labeling reaction was started with 100 ng total-RNA per sample. For labeling dephosphorylated RNA, T4 RNA ligase, incorporating Cyanine 3-Cytidine biphosphate (miRNA Complete Labeling and Hyb Kit, Agilent Technologies, Santa Clara, USA) was used. The Cyanine-3-labeled miRNA samples were then prepared for One-Color based hybridization (Complete miRNA Labeling and Hyb Kit, Agilent Technologies, Santa Clara, USA). Hybridization was performed at 55°C for 20 hrs with Human miRNA Microarrays Release 16.0, 8x60K format (Agilent Technologies, Santa Clara, USA). Microarray slides were washed (Gene Expression Wash Buffers, Agilent Technologies, Santa Clara) and dried with acetonitrile (Sigma-Aldich, St.Louis, USA). Fluorescent signal intensities were detected with Agilent DNA Microarray Scanner (Agilent Technologies, Santa Clara, USA) and Scan Control A.8.4.1 Software (Agilent Technologies, Santa Clara, USA). Extraction of data was done by using the Feature Extraction 10.7.3.1 Software (Agilent Technologies, Santa Clara, USA).