Neutrophil gelatinase-associated lipocalin as a survival factor.
NGAL (human neutrophil gelatinase-associated lipocalin) and its mouse analogue 24p3 are members of the lipocalin family of small secreted proteins. These proteins are up-regulated in a number of pathological conditions, including cancers, and may function as transporters of essential factors. Although previous publications have suggested that 24p3 has pro-apoptotic functions, other data are more suggestive of a survival function. The current study was designed to determine whether NGAL is pro- or anti-apoptotic. Apoptosis induced in human adenocarcinoma A549 cells by the 5-lipoxygenase-activating-protein inhibitor MK886, or several celecoxib-derived PDK1 (phosphoinositide-dependent kinase 1) inhibitors that are devoid of cyclo-oxygenase-2 inhibitory activity, was accompanied by a dose- and time-dependent increase of NGAL mRNA levels, as was reported previously with 24p3. A similar induction of NGAL mRNA was observed in human breast cancer MCF7 cells treated with MK886, indicating this was not a cell-specific effect. Treatment of A549 cells with up to 150 mug/10(6) cells of purified recombinant NGAL protein had no effect on viability, whereas antisera against the full-length NGAL protein induced apoptosis in these cells. The stable overexpression of NGAL in A549 cells had no effect on proliferation or viability. However, the cell death induced by a PDK1 inhibitor was reduced by 50% in NGAL-overexpressing cells. Decreasing NGAL mRNA and protein expression with siRNA (small interfering RNA) in A549 cells increased the toxicity of a PDK1 inhibitor by approx. 45%. These data indicate that, although the induction of NGAL correlates with apoptosis, this induction represents a survival response. Because NGAL is a secreted protein, it may play an extracellular role in cell defence against toxicants and/or facilitate the survival of the remaining cells.
Tong
Zhimin
Z
Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA. zhimin@mail.utexas.edu
Wu
Xuli
X
Ovcharenko
Dmitriy
D
Zhu
Jiuxiang
J
Chen
Ching-Shih
CS
Kehrer
James P
JP
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000209:Acute-Phase Proteins / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D000071068:Lipocalin-2; D054834:Lipocalins; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology / Q000633:toxicity; D012333:RNA, Messenger / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology / Q000633:toxicity; D015854:Up-Regulation / Q000187:drug effects; D002722:Chlorobenzenes
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000209:Acute-Phase Proteins; D007211:Indoles; D000071068:Lipocalin-2; D054834:Lipocalins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D011720:Pyrazoles; D012333:RNA, Messenger; D013449:Sulfonamides; C489506:LCN2 protein, human; C500894:OSU 03012; C060893:MK-886; D002722:Chlorobenzenes; C578562:PDPK1 protein, human; C578564:Pdpk1 protein, mouse