Reciprocal expression of pleiotrophin and midkine in normal versus malignant lung tissues

Abundant evidence suggests that growth factors are important mediators of non-small cell lung cancer (NSCLC) growth. Although multiple growth factors have been found to be produced by NSCLC tissues, little is known about possible differences in growth factor expression between malignant and adjacent normal lung tissues. Variation in growth factor expression between normal and malignant lung tissues could be potentially useful diagnostically and therapeutically. In studies reported here, the expression of the angiogenic growth factor pleiotrophin (PTN) and homolog midkine (MK) was assessed in resected normal and malignant lung tissues. Primers specific for the two growth factors were used to amplify reverse transcriptase-produced DNA copies of RNA transcripts harvested from the tissues. This analysis revealed that all normal lung tissues examined (n = 17) expressed PTN but only two expressed MK. Conversely, all of the resected lung cancers (n = 20) expressed MK but only one expressed PTN. These results demonstrated a striking reciprocal expression pattern of MK and PTN in normal versus malignant lung tissue.