ELEVATED EXPRESSION OF THE NEUTROPHIL CALCIUM-BINDING PROTEIN, MRP-14, IN METASTASIS-ENHANCING NEUTROPHILS

Tumor-elicited neutrophils (tcPMN) purified from 13762NF mammary adeno carcinoma tumor-bearing rats enhanced metastasis of syngeneic cells wh en co-injected intravenously; whereas, circulating (cPMN) and phorbol ester-activated (PMA-PMN) neutrophils did not [Welch et al. (1989) Pro c. Natl. Acad. Sci. 86:5859-63]. We hypothesized that different protei n expression was responsible for functional differences between the ne utrophil subtypes. Two-dimensional polyacrylamide gel electrophoresis was used to compare neutrophils (cPMN, PMA-PMN) purified from the peri pheral blood of healthy, syngeneic nontumor-bearing rats, to tcPMN col lected from rats with highly metastatic [clone MTLn3, subclone MTLn3(T 44).5] or poorly metastatic [subclone MTLn3(T44).11] tumors growing in the mammary fat pads. Quantitative differences in polypeptide express ion were observed between these functionally distinct PMN populations. Compared to cPMN, expression of a M(r) approximate to 38.8 kDa (pI ap proximate to 8) polypeptide was similar in tcPMN collected from poorly metastatic tumor-bearing rats, higher in PMA-PMN, and further increas ed in tcPMN from rats with highly metastatic tumors. Expression of two polypeptides, M(r) approximate to 14.1 kDa (pl approximate to 6) and M(r) approximate to 43.3 kDa (pl approximate to 5), was greater in tcP MN from rats with highly metastatic tumors compared to cPMN, PMA-PMN, or tcPMN from rats bearing poorly metastatic tumors. The latter two po lypeptides thus appeared to be specifically increased in tcPMN from ra ts bearing highly metastatic tumors. Because it was most abundant and displayed the greatest differences between PMN subtypes, the M(r) appr oximate to 14.1 kDa protein was further analyzed. Tryptic digests foll owed by internal sequence analyses of resulting peptide fragments reve aled that the M(r) approximate to 14.1 kDa contained amino acid sequen ces that were identical to those of MRP-14, a 14 kDa neutrophil calciu m-binding protein belonging to the S-100 protein family of calcium-bin ding proteins. These results suggest a novel function for MRP-14 and s uggest that MRP-14 may represent a marker for distinguishing phenotypi cally distinct subpopulations of neutrophils, particularly tcPMN with metastasis-enhancing abilities.