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J. Biol. Chem., Vol. 280, Issue 15, 14923-14931, April 15, 2005

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Manduca sexta Serpin-4 and Serpin-5 Inhibit the Prophenol Oxidase Activation Pathway

cDNA CLONING, PROTEIN EXPRESSION, AND CHARACTERIZATION^*

Youren Tong and Michael R. Kanost

From the Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506

Infection stimulates the innate immune responses of insects, including activation of prophenol oxidase (pro-PO) in plasma as the last step of a serine protease cascade. To investigate the roles of protease inhibitors in regulating this pathway, we cloned cDNAs for two new serpins (serpin-4 and serpin-5) from the tobacco hornworm, Manduca sexta. Serpin-4 and serpin-5 mRNAs are constitutively expressed at a low level in larval hemocytes and fat body and increased dramatically upon bacterial challenge. These serpins are present in larval plasma at 3 (serpin-4) and 1 µg/ml (serpin-5) and increased 3–8-fold by 24 h after injection of bacteria or fungi. Recombinant serpin-4 and serpin-5 decreased pro-PO activation when added to plasma, but they did not directly inhibit the pro-PO-activating proteases. Instead, they apparently regulate the pathway by inhibiting one or more target proteases upstream of the pro-PO-activating proteases.

Received for publication, January 14, 2005 , and in revised form, January 27, 2005.

^* This work was supported by National Institutes of Health Grant GM41247. This is contribution 05-218-J from the Kansas Agricultural Experiment Station. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AY566162, AY566163, AY566166, and AY566167.

To whom correspondence should be addressed. Tel.: 785-532-6964; Fax: 785-532-7278; E-mail: kanost{at}ksu.edu.

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