The combined effect of tumor-produced parathyroid hormone-related protein and transforming growth factor-alpha enhance hypercalcemia in vivo and bone resorption in vitro.
Humoral hypercalcemia of malignancy is a multifactorial syndrome caused by the action of tumor-produced factors on target organs of bone, kidney, and intestine to disrupt normal calcium homeostasis. Although parathyroid hormone-related protein (PTHrP) plays an integral role in the syndrome, tumors also produce other hypercalcemic factors, such as transforming growth factor-alpha (TGF-alpha), which may modulate the effects of PTHrP. In order to determine if the effects of PTHrP on calcium homeostasis can be modulated by TGF-alpha, we have used a human squamous cell carcinoma cell line (RWGT2) which produces PTHrP alone and Chinese hamster ovarian (CHO) cells expressing only transfected human TGF-alpha complementary DNA (CHO/TGF-alpha). We studied the effects of these tumors on calcium homeostasis in nude mice bearing both tumors or each tumor alone. Whole blood ionized calcium concentrations (mean +/- SEM in mmol/L) were significantly higher in mice bearing both RWGT2 and CHO/TGF-alpha tumors (3.11 +/- 0.06, P < 0.05) when compared with mice bearing either RWGT2 alone (2.02 +/- 0.06), CHO/TGF-alpha alone (1.42 +/- 0.01), or RWGT2 and nontransfected CHO tumors (1.86 +/- 0.01). This enhanced effect was also observed using continuous PTHrP-(1-34) infusion (2 micrograms/day) in mice bearing CHO/TGF-alpha tumors. In addition, tumor cell conditioned media was tested for bone resorbing activity in organ cultures of fetal rat long bones previously incorporated with 45calcium (45Ca++). Conditioned medium at 0.1% (vol/vol) from either RWGT2 or CHO/TGF-alpha had no bone resorbing activity over control (%45Ca++ release, mean +/- SEM; control 23 +/- 1, RWGT2 19 +/- 1, CHO/TGF-alpha 23 +/- 1). However, the combination of 0.1% conditioned medium from RWGT2 and CHO/TGF-alpha significantly increased bone resorption (53 +/- 2, P < 0.05). These data demonstrate that the hypercalcemic effects of tumor-produced PTHrP are enhanced by TGF-alpha and that this effect may be due to increased bone resorption.
Guise
T A
TA
Department of Medicine, University of Texas Health Science Center, San Antonio 78284-7877.
Yoneda
T
T
Yates
A J
AJ
Mundy
G R
GR
D000818:Animals; D001862:Bone Resorption; D001842:Bone and Bones / Q000196:embryology / Q000502:physiology; D016466:CHO Cells; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology; D006224:Cricetinae; D017077:Culture Media, Conditioned; D006801:Humans; D006934:Hypercalcemia / Q000209:etiology*; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008875:Middle Aged; D009369:Neoplasms / Q000150:complications*; D044162:Parathyroid Hormone-Related Protein; D014176:Protein Biosynthesis; D011506:Proteins / Q000494:pharmacology*; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology; D014162:Transfection; D016211:Transforming Growth Factor alpha / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; C470121:PTHLH protein, human; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D011994:Recombinant Proteins; D016211:Transforming Growth Factor alpha