PMC

Folliculin (FLCN) immunostaining in normal kidney, and Birt–Hogg–Dubé (BHD) and sporadic tumors. (a) H&E staining of a normal kidney. (b) Serial section of sample A immunostained for FLCN. Nuclei of distal tubules were strongly positive for FLCN. (c–h) Immunostaining for FLCN in BHD and sporadic tumors. Weak cytoplasmic staining was evident in tumors of BHD patients (c, e, h). Insets highlight distal tubules of non-tumor areas, showing immunoreactivity to FLCN. Sporadic renal tumors (d, f, h) showed strong nuclear staining.

Glycoprotein non-metastatic B (GPNMB) immunostaining of Birt–Hogg–Dubé (BHD) and sporadic tumors. (a, c, e) H&E staining of BHD tumors (T) of patients BHD2-T1 (a), BHD13-T1 (c), and a nodule of oncocytosis in the normal-looking region (N) of BHD13 (e, dotted circle). (b, d, f) Serial sections of (a, c, e) immunostained for GPNMB. Tumor cells (b, d) were intensely stained for GPNMB. Tubules of normal-looking regions were negative for GPNMB. GPNMB was immunostained in the region of focal oncocytosis (f, dotted circle). (g–i) Immunostaining for GPNMB in sporadic renal tumors: papillary renal cell carcinoma (g), oncocytoma (h), and chromophobe renal cell carcinoma (i). Insets are H&E stains of the serial sections.

Folliculin (FLCN) expression in Birt–Hogg–Dubé (BHD) and sporadic tumors. (a) Representative results of Western blot analysis of BHD kidneys. Patients BHD9 and BHD17 had two independent tumors (T1, T2). The FLCN bands (70 kDa) were clearly detected in non-tumor lanes but barely seen in tumor lanes. N, normal-looking region; T, tumor region. (b) Representative results of Western blotting analysis of sporadic renal tumors and normal kidneys without the background of BHD. Sporadic renal tumors include clear cell renal cell carcinomas (RCCs) (n = 3), oncocytoma (n = 1), papillary RCC (n = 1), and chromophobe RCCs (n = 3).

Germline and somatic mutation patterns of FLCN. (a) Birt–Hogg–Dubé (BHD) syndrome patient BHD9 carried FLCN germline mutation in exon 11 (upper left). The exon 10 sequence was confirmed to be wild-type (lower left). The patient's tumor BHD9-T2 showed somatic mutation in exon 10 (lower right) in addition to germline mutation (upper right). (b) BHD17 carried FLCN germline mutation in exon 11 (left). The mutation pattern was c.1285dupC. In the tumor lesion, heterozygous mutation in the C8 tract was completely replaced by a C9 tract, indicating loss of heterozygosity (right). No additional mutation was found in the other exons. Arrows indicate starting point of mutation.

Histological and gross features of FLCN-related renal tumors. (a, b) H&E staining of chromophobe renal cell carcinoma (RCC) in Birt–Hogg–Dubé (BHD) syndrome patient BHD13 (a) and hybrid oncocytic/chromophobe tumor (HOCT) in BHD5 (b). A few benign-looking cystic tubules migrated in tumor nodules (arrows). (c, d) High magnification of chromophobe RCC in BHD17 (c) and HOCT in BHD10 (d). HOCT is composed of oncocytoma-like granular cells with round nuclei and chromophobe RCC-like cell borders and perinuclear halo. (e) Sectioned surface of BHD7 shows a brownish solid tumor. (f, g) H&E staining of papillary RCC in BHD7 at low magnification (f) and high magnification (g). (h) Tumor cells were diffusely immunostained for α-methylacyl-CoA racemase, supporting the histology of papillary RCC.

Glycoprotein non-metastatic B (GPNMB) expression in Birt–Hogg–Dubé (BHD) and sporadic tumors. (a) Expression levels of GPNMB mRNA were analyzed by quantitative RT-PCR as shown. Sporadic renal tumors include clear cell renal cell carcinomas (RCCs) (n = 9), oncocytoma (n = 1), papillary RCC (n = 1), and chromophobe RCCs (n = 6). (b) Representative results of Western blot analysis of BHD kidneys. Patients BHD9 and BHD17 had two independent tumors (T1, T2), respectively. Two isoforms (115 kDa and 80 kDa) of GPNMB bands were seen in tumor lanes, but not in normal-looking lanes. N, normal-looking region; T, tumor region. (c) Representative results of Western blot analysis of sporadic renal tumors and normal kidneys without the background of BHD. GPNMB bands were barely seen in sporadic tumor and normal kidney lanes. Sporadic renal tumors included clear cell RCCs (n = 3), oncocytoma (n = 1), papillary RCC (n = 1), and chromophobe RCCs (n = 4). PC, positive control using BHD9-T2.