Table II. Type II membrane proteins which are significantly altered in secretomes of Sppl3^−/− MEF. Table contains all membrane proteins with type-II orientation which are significantly altered upon Sppl3 knockout. Those type II proteins that were less abundantly secreted from Sppl3^−/− MEF compared to control cells are shown above the dotted line, those secreted more below. Indicated are the names of the proteins, the gene name, number of unique peptides, the mean of the ratio between Sppl3 knockout (KO) and control (wt) of five biological replicates and the p value calculated with a heteroscedastic, two-sided student's t-test based on the log2 transformed intensity ratios between the control and the SPPL3 overexpression condition. Previously published SPPL3 substrates are highlighted in bold, those identified also in the HEK293 SPPL3 overexpression screen (Fig. 1 and Table I) in italics.

Protein names	Gene names	Unique peptides	Mean Sppl3 KO/wt	p value
Alpha-mannosidase 2	Man2a1	25	0.03	1.19E-11
Alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase A	Mgat5	13	0.06	6.60E-08
Agrin	Agrn	30	0.04	7.97E-07
Soluble calcium-activated nucleotidase 1	Cant1	6	0.11	3.26E-05
Protein FAM198B	Fam198b	14	0.21	8.12E-05
Carbohydrate sulfotransferase 14	Chst14	11	0.29	1.23E-04
N-acetyllactosaminide beta-1,3-N-acetylglucosaminyltransferase	B3gnt1	5	0.26	1.36E-04
Alpha-1,6-mannosyl-glycoprotein 2-beta-N-acetylglucosaminyltransferase	Mgat2	8	0.32	7.14E-04
Heparan-sulfate 6-O-sulfotransferase 1	Hs6st1	4	0.31	8.63E-04
Beta-1,3-galactosyl-O-glycosyl-glycoprotein beta-1,6-N-acetylglucosaminyltransferase	Gcnt1	6	0.45	1.21E-03
N-acetylated-alpha-linked acidic dipeptidase 2	Naalad2	12	0.27	1.26E-03
Alpha-1,3-mannosyl-glycoprotein 2-beta-N-acetylglucosaminyltransferase	Mgat1	5	0.28	2.74E-03
Beta-galactoside alpha-2,6-sialyltransferase 1	St6gal1	4	0.34	5.02E-03
Carbohydrate sulfotransferase 12	Chst12	3	0.21	5.04E-03
UDP-GalNAc:beta-1,3-N-acetylgalactosaminyltransferase 1	B3galnt1	2	0.35	6.25E-03
Alpha-mannosidase 2x	Man2a2	6	0.51	9.39E-03
Beta-1,4-galactosyltransferase 5	B4galt5	4	0.33	1.02E-02
4F2 cell-surface antigen heavy chain	Slc3a2	11	0.40	1.14E-02
Beta-1,4 N-acetylgalactosaminyltransferase 1	B4galnt1	6	0.44	1.16E-02
Mannosidase, alpha, class 1C	Man1c1	6	0.53	1.27E-02
Beta-1,4-galactosyltransferase 1	B4galt1	4	0.52	1.36E-02
Beta-1,3-N-acetylglucosaminyltransferase lunatic fringe	Lfng	4	0.46	1.62E-02
Polypeptide N-acetylgalactosaminyltransferase 10	Galnt10	8	0.27	1.69E-02
UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 9	B3gnt9	4	0.34	2.13E-02
Bifunctional heparan sulfate N-deacetylase/N-sulfotransferase 1	Ndst1	5	0.63	2.37E-02
Integral membrane protein 2B	Itm2b	2	0.70	2.43E-02
Exostosin-like 2	Extl2	4	0.61	3.17E-02
Golgi membrane protein 1	Golm1	5	0.34	3.42E-02
Heparan-sulfate 6-O-sulfotransferase 2	Hs6st2	9	0.68	4.28E-02
Aminopeptidase N	Anpep	15	58.36	3.70E-10
Collectin-12	Colec12	10	4.44	2.98E-03