Alterations in the mitochondrial displacement loop in lung cancers.
OBJECTIVE
Alterations of the noncoding displacement (D) loop of mitochondrial DNA are present in many cancers. These alterations include numerical changes in a homopolymeric C tract (PCT) at positions 303-309 and single base substitutions (SBS). We determined the frequency of D-loop alterations in lung cancer cell lines and tumors, and related them to clinicopathologic features.


METHODS
We sequenced the entire D-loop of 28 lung cancer cell lines [12 small cell lung cancer (SCLC) and 16 non-small cell lung cancer (NSCLC)] and matched B-lymphoblastoid cell lines. In 55 resected NSCLCs and corresponding nonmalignant lungs we determined the length of the PCT.


RESULTS
In nonmalignant cell lines and tissues the most frequent PCT repeat number was seven (36 of 83; 43%) with a range of six to nine. Alterations, often multiple, were present in 17 of 28 (61%) of the cell lines, including 8 of 12 SCLC (67%) and 9 of 16 NSCLC (56%) lines. They consisted of SBS in 8 of 28 lines (29%), all of which were homoplasmic, and PCT changes in 14 of 28 (50%) lines, 8 of which were homoplasmic. Of interest, 95% (40 of 42) of the SBS were present within the two hypervariable regions in the D-loop. Because SBS were more frequent if PCT changes were present, only the PCT number was determined in resected samples. PCT changes were present in 11 of 55 (20%) of the NSCLC tumors. Changes were never noted in tumors when the PCT number in the nonmalignant tissue was seven, and only two tumor cell lines had changes when the PCT number in the matched lymphoblastoid cell line was seven. These changes were higher in squamous cell carcinomas (8 of 25; 32%) than in adenocarcinomas (3 of 30; 10%; P = 0.04) and in large tumors (T3 and T4; 7 of 20; 35%) compared with smaller tumors (T1 and T2; 4 of 35; 11%; P = 0.04). Smoking history, gender, age, and stage were not related to frequency of PCT change.


CONCLUSIONS
Our findings indicate that D-loop alterations are frequent in lung cancers and their cell lines, and that these changes are weakly associated with certain clinical parameters. In tumors PCT changes were only present when the corresponding nonmalignant lung demonstrated a variation from the most common repeat number of seven.
Suzuki
Makoto
M
Hamon Center for Therapeutic Oncology Research, University of Texas Southwestern Medical Center, Dallas Texas 75390, USA.
Toyooka
Shinichi
S
Miyajima
Kuniharu
K
Iizasa
Toshihiko
T
Fujisawa
Takehiko
T
Bekele
Nebiyou B
NB
Gazdar
Adi F
AF
D000230:Adenocarcinoma / Q000235:genetics / Q000473:pathology / Q000601:surgery; D000368:Aged; D001483:Base Sequence; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000601:surgery; D018288:Carcinoma, Small Cell / Q000235:genetics / Q000473:pathology / Q000601:surgery; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000473:pathology / Q000601:surgery; D017931:DNA Primers; D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D006801:Humans; D008168:Lung / Q000473:pathology; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009154:Mutation; D012907:Smoking
D017931:DNA Primers; D004272:DNA, Mitochondrial